diff --git a/README.md b/README.md
index 96655b69..32f4a29c 100644
--- a/README.md
+++ b/README.md
@@ -5,6 +5,7 @@ It supports registering, verifying, sending and receiving messages.
 signal-cli uses a [patched libsignal-service-java](https://github.com/Turasa/libsignal-service-java),
 extracted from the [Signal-Android source code](https://github.com/signalapp/Signal-Android/tree/main/lib/libsignal-service).
 For registering you need a phone number where you can receive SMS or incoming calls.
+Existing accounts without a phone number can be linked from a compatible Signal mobile app.
 
 signal-cli is primarily intended to be used on servers to notify admins of important events.
 For this use-case, it has a daemon mode with JSON-RPC interface ([man page](https://github.com/AsamK/signal-cli/blob/master/man/signal-cli-jsonrpc.5.adoc))
@@ -60,14 +61,16 @@ For a complete usage overview please read
 the [man page](https://github.com/AsamK/signal-cli/blob/master/man/signal-cli.1.adoc) and
 the [wiki](https://github.com/AsamK/signal-cli/wiki).
 
-Important: The ACCOUNT is your phone number in international format and must include the country calling code. Hence it
+For a numbered account, ACCOUNT is your phone number in international format and must include the country calling code. Hence it
 should start with a "+" sign. (See [Wikipedia](https://en.wikipedia.org/wiki/List_of_country_calling_codes) for a list
 of all country codes.)
+For a linked account without a phone number, use its ACI (Account ID) instead.
+See [numberless accounts](doc/numberless-accounts.md) for details.
 
 * Link to an existing account
 
-  If you have an existing Signal account associated
-  with a number, you can link signal-cli to it with:
+  If you have an existing Signal account, with or without a phone number,
+  you can link signal-cli to it with:
 
       signal-cli link
 
diff --git a/doc/numberless-accounts.md b/doc/numberless-accounts.md
new file mode 100644
index 00000000..e4b7e752
--- /dev/null
+++ b/doc/numberless-accounts.md
@@ -0,0 +1,46 @@
+# Linking an account without a phone number
+
+This branch adds secondary-device linking for accounts registered without a phone
+number, such as those created in Signal Android 8.28. It does not implement creating
+or recovering a primary numberless account using an Account Key.
+
+Run `signal-cli link -n signal-cli`, then scan the QR code from the mobile app's
+Linked devices screen. The linking URI advertises `capabilities=nopni`. If linking
+completes, the CLI prints the account's ACI instead of a phone number.
+
+Use that ACI with `-a` for subsequent commands:
+
+```sh
+signal-cli -a YOUR_ACCOUNT_ACI receive
+signal-cli -a YOUR_ACCOUNT_ACI listGroups
+signal-cli -a YOUR_ACCOUNT_ACI send --note-to-self -m 'Numberless account test'
+```
+
+When only one local account exists, `-a` can be omitted. Numbered accounts continue
+to accept their phone number or ACI. A numberless account cannot infer a country
+code for a recipient's phone number; use a complete international number beginning
+with `+`, an ACI, or a Signal username.
+
+In JSON-RPC, use the ACI in the `account` parameter. `listAccounts` and `finishLink`
+return an `aci` field alongside `number`; `number` is null for a numberless account.
+Receive events use the ACI in their `account` field when there is no phone number.
+REST wrappers must understand those nullable numbers and ACI selectors before they
+can be assumed compatible.
+
+## Validation
+
+Run `./gradlew test installDist` with JDK 25. Regression tests cover the linking
+request (including ACI authentication and omission of PNI keys), numbered-account
+linking, missing group credential salts, persisted account reload, account discovery,
+group membership lookup, recipient-number formatting, and JSON account identifiers.
+
+Live acceptance requires a real mobile account and is separate from these tests:
+
+1. Link a newly created secondary device using the numberless mobile account.
+2. Restart signal-cli and verify that `listAccounts` still reports the ACI.
+3. Send and receive a Note to Self message and a DM with a second account.
+4. Receive a group message, list the group, and send a reply to that test group.
+5. Run the JSON-RPC daemon, restart it, and repeat receiving and sending by ACI.
+
+Only one signal-cli process may open an account's state at a time. Stop the daemon
+before running one-off commands against the same configuration directory.
diff --git a/lib/src/main/java/org/asamk/signal/manager/Manager.java b/lib/src/main/java/org/asamk/signal/manager/Manager.java
index 7d0c73af..82d42eda 100644
--- a/lib/src/main/java/org/asamk/signal/manager/Manager.java
+++ b/lib/src/main/java/org/asamk/signal/manager/Manager.java
@@ -98,6 +98,14 @@ public interface Manager extends Closeable {
 
     String getSelfACI();
 
+    /**
+     * Returns the phone number for numbered accounts, or the ACI for numberless accounts.
+     */
+    default String getSelfIdentifier() {
+        final var number = getSelfNumber();
+        return number != null ? number : getSelfACI();
+    }
+
     /**
      * This is used for checking a set of phone numbers for registration on Signal
      *
diff --git a/lib/src/main/java/org/asamk/signal/manager/ProvisioningManager.java b/lib/src/main/java/org/asamk/signal/manager/ProvisioningManager.java
index 09a329f5..bcff5ac0 100644
--- a/lib/src/main/java/org/asamk/signal/manager/ProvisioningManager.java
+++ b/lib/src/main/java/org/asamk/signal/manager/ProvisioningManager.java
@@ -10,5 +10,8 @@ public interface ProvisioningManager {
 
     URI getDeviceLinkUri() throws TimeoutException, IOException;
 
+    /**
+     * Completes linking and returns the account's phone number, or ACI if it has no number.
+     */
     String finishDeviceLink(String deviceName) throws IOException, TimeoutException, UserAlreadyExistsException;
 }
diff --git a/lib/src/main/java/org/asamk/signal/manager/SignalAccountFiles.java b/lib/src/main/java/org/asamk/signal/manager/SignalAccountFiles.java
index d5856d97..231aacc7 100644
--- a/lib/src/main/java/org/asamk/signal/manager/SignalAccountFiles.java
+++ b/lib/src/main/java/org/asamk/signal/manager/SignalAccountFiles.java
@@ -65,15 +65,25 @@ public class SignalAccountFiles {
         return accountsStore.getAllNumbers();
     }
 
+    public Set<String> getAllLocalAccountIdentifiers() throws IOException {
+        return accountsStore.getAllAccounts().stream()
+                .map(a -> a.number() != null ? a.number() : a.uuid())
+                .collect(java.util.stream.Collectors.toSet());
+    }
+
     public MultiAccountManager initMultiAccountManager() throws IOException {
         final var managerPairs = accountsStore.getAllAccounts().parallelStream().map(a -> {
+            final var identifier = a.number() != null ? a.number() : a.uuid();
             try {
-                return new Pair<Manager, Throwable>(initManagerByNumber(a.number(), a.path()), null);
+                final var manager = a.number() != null
+                        ? initManagerByNumber(a.number(), a.path())
+                        : initManagerByAci(ACI.parseOrThrow(a.uuid()), a.path());
+                return new Pair<Manager, Throwable>(manager, null);
             } catch (NotRegisteredException e) {
-                logger.warn("Ignoring {}: {} ({})", a.number(), e.getMessage(), e.getClass().getSimpleName());
+                logger.warn("Ignoring {}: {} ({})", identifier, e.getMessage(), e.getClass().getSimpleName());
                 return null;
             } catch (AccountCheckException | IOException e) {
-                logger.error("Failed to load {}: {} ({})", a.number(), e.getMessage(), e.getClass().getSimpleName());
+                logger.error("Failed to load {}: {} ({})", identifier, e.getMessage(), e.getClass().getSimpleName());
                 return new Pair<Manager, Throwable>(null, e);
             }
         }).filter(Objects::nonNull).toList();
diff --git a/lib/src/main/java/org/asamk/signal/manager/helper/AccountHelper.java b/lib/src/main/java/org/asamk/signal/manager/helper/AccountHelper.java
index 5f208ede..2dfc4cac 100644
--- a/lib/src/main/java/org/asamk/signal/manager/helper/AccountHelper.java
+++ b/lib/src/main/java/org/asamk/signal/manager/helper/AccountHelper.java
@@ -18,6 +18,7 @@ import org.signal.core.models.ServiceId.ACI;
 import org.signal.core.models.ServiceId.PNI;
 import org.signal.core.util.Base64;
 import org.signal.core.util.crypto.DeviceNameCipher;
+import org.signal.libsignal.net.RequestResult;
 import org.signal.libsignal.protocol.IdentityKeyPair;
 import org.signal.libsignal.protocol.InvalidKeyException;
 import org.signal.libsignal.protocol.NoSessionException;
@@ -27,6 +28,7 @@ import org.signal.libsignal.protocol.state.SignedPreKeyRecord;
 import org.signal.libsignal.protocol.util.KeyHelper;
 import org.signal.libsignal.usernames.BaseUsernameException;
 import org.signal.libsignal.usernames.Username;
+import org.signal.network.api.AccountApiV2;
 import org.signal.network.exceptions.NonSuccessfulResponseCodeException;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
@@ -57,11 +59,13 @@ import java.util.Objects;
 import java.util.UUID;
 import java.util.concurrent.TimeUnit;
 
+import kotlin.Unit;
 import okio.ByteString;
 
 import static org.asamk.signal.manager.config.ServiceConfig.PREKEY_MAXIMUM_ID;
 import static org.asamk.signal.manager.util.Utils.handleResponseException;
 import static org.asamk.signal.manager.util.Utils.handleResponseExceptionSuspend;
+import static org.asamk.signal.manager.util.Utils.runSuspendBlocking;
 import static org.whispersystems.signalservice.internal.util.Util.isEmpty;
 
 public class AccountHelper {
@@ -96,10 +100,10 @@ public class AccountHelper {
             } else {
                 context.getPreKeyHelper().refreshPreKeysIfNecessary();
             }
-            if (account.getPni() == null) {
+            if (account.getPni() == null && account.getNumber() != null) {
                 checkWhoAmiI();
             }
-            if (!account.isPrimaryDevice() && account.getPniIdentityKeyPair() == null) {
+            if (!account.isPrimaryDevice() && account.getPni() != null && account.getPniIdentityKeyPair() == null) {
                 throw new IOException("Missing PNI identity key, relinking required");
             }
             if (account.getPreviousStorageVersion() < 10
@@ -138,8 +142,9 @@ public class AccountHelper {
         final var whoAmI = dependencies.getAccountManager().getWhoAmI();
         final var number = whoAmI.getNumber();
         final var aci = ACI.parseOrThrow(whoAmI.getAci());
-        final var pni = PNI.parseOrThrow(whoAmI.getPni());
-        if (number.equals(account.getNumber()) && aci.equals(account.getAci()) && pni.equals(account.getPni())) {
+        final var pni = whoAmI.getPni() == null ? null : PNI.parseOrThrow(whoAmI.getPni());
+        if (Objects.equals(number, account.getNumber()) && aci.equals(account.getAci())
+                && Objects.equals(pni, account.getPni())) {
             return;
         }
 
@@ -150,7 +155,7 @@ public class AccountHelper {
         account.setNumber(number);
         account.setAci(aci);
         account.setPni(pni);
-        if (account.isPrimaryDevice() && account.getPniIdentityKeyPair() == null) {
+        if (pni != null && account.isPrimaryDevice() && account.getPniIdentityKeyPair() == null) {
             account.setPniIdentityKeyPair(KeyUtils.generateIdentityKeyPair());
         }
         account.getRecipientTrustedResolver().resolveSelfRecipientTrusted(account.getSelfRecipientAddress());
@@ -564,7 +569,20 @@ public class AccountHelper {
     }
 
     public void updateAccountAttributes() throws IOException {
-        handleResponseException(dependencies.getAccountApi().setAccountAttributes(account.getAccountAttributes(null)));
+        if (account.getNumber() != null) {
+            handleResponseException(dependencies.getAccountApi().setAccountAttributes(account.getAccountAttributes(null)));
+            return;
+        }
+        final var api = new AccountApiV2(dependencies.getAuthenticatedSignalWebSocket());
+        final RequestResult<Unit, ? extends AccountApiV2.SetAccountAttributesError> result =
+                runSuspendBlocking(cont -> api.setAccountAttributes(account.getAccountAttributesV2(), cont));
+        if (result instanceof RequestResult.NonSuccess<?> failure) {
+            if (failure.getError() instanceof AccountApiV2.SetAccountAttributesError.Unauthorized) {
+                throw new AuthorizationFailedException(401, "Authorization failed!");
+            }
+            throw new IOException("Account attribute update rate limited; try again later");
+        }
+        handleResponseException(result);
     }
 
     public void addDevice(DeviceLinkUrl deviceLinkInfo) throws IOException, org.asamk.signal.manager.api.DeviceLimitExceededException {
diff --git a/lib/src/main/java/org/asamk/signal/manager/helper/GroupV2Helper.java b/lib/src/main/java/org/asamk/signal/manager/helper/GroupV2Helper.java
index 6bbe6971..0ed6d4b2 100644
--- a/lib/src/main/java/org/asamk/signal/manager/helper/GroupV2Helper.java
+++ b/lib/src/main/java/org/asamk/signal/manager/helper/GroupV2Helper.java
@@ -136,7 +136,7 @@ class GroupV2Helper {
 
     int findRevisionWeWereAdded(DecryptedGroup partialDecryptedGroup) {
         ByteString aciBytes = getSelfAci().toByteString();
-        ByteString pniBytes = getSelfPni().toByteString();
+        ByteString pniBytes = getSelfPni() == null ? null : getSelfPni().toByteString();
         for (DecryptedMember decryptedMember : partialDecryptedGroup.members) {
             if (decryptedMember.aciBytes.equals(aciBytes) || decryptedMember.pniBytes.equals(pniBytes)) {
                 return decryptedMember.joinedAtRevision;
@@ -264,7 +264,7 @@ class GroupV2Helper {
         var pendingMembersList = groupInfoV2.getGroup().pendingMembers;
         final var selfAci = getSelfAci();
         var selfPendingMember = DecryptedGroupUtil.findPendingByServiceId(pendingMembersList, selfAci);
-        if (selfPendingMember.isEmpty()) {
+        if (selfPendingMember.isEmpty() && getSelfPni() != null) {
             selfPendingMember = DecryptedGroupUtil.findPendingByServiceId(pendingMembersList, getSelfPni());
         }
 
diff --git a/lib/src/main/java/org/asamk/signal/manager/helper/IncomingMessageHandler.java b/lib/src/main/java/org/asamk/signal/manager/helper/IncomingMessageHandler.java
index 6aa9c5a0..7af7b28c 100644
--- a/lib/src/main/java/org/asamk/signal/manager/helper/IncomingMessageHandler.java
+++ b/lib/src/main/java/org/asamk/signal/manager/helper/IncomingMessageHandler.java
@@ -339,7 +339,7 @@ public final class IncomingMessageHandler {
             throw new AssertionError(e);
         }
 
-        if (account.getPni().equals(destination.serviceId)) {
+        if (destination.serviceId.equals(account.getPni())) {
             account.getRecipientStore().markNeedsPniSignature(sender, true);
         } else if (account.getAci().equals(destination.serviceId)) {
             account.getRecipientStore().markNeedsPniSignature(sender, false);
@@ -1124,7 +1124,7 @@ public final class IncomingMessageHandler {
         if (destination == null || destination.isUnknown()) {
             throw new InvalidMessageException("Missing destination");
         }
-        if (!account.getAci().equals(destination) && !account.getPni().equals(destination)) {
+        if (!destination.equals(account.getAci()) && !destination.equals(account.getPni())) {
             throw new InvalidMessageException("Message not intended for this account");
         }
         return new DeviceAddress(account.getRecipientResolver().resolveRecipient(destination),
diff --git a/lib/src/main/java/org/asamk/signal/manager/helper/SendHelper.java b/lib/src/main/java/org/asamk/signal/manager/helper/SendHelper.java
index dd057c23..9564830c 100644
--- a/lib/src/main/java/org/asamk/signal/manager/helper/SendHelper.java
+++ b/lib/src/main/java/org/asamk/signal/manager/helper/SendHelper.java
@@ -886,7 +886,8 @@ public class SendHelper {
 
         var address = context.getRecipientHelper().resolveSignalServiceAddress(recipientId);
         try {
-            final boolean includePniSignature = account.getRecipientStore().needsPniSignature(recipientId);
+            final boolean includePniSignature = account.getPni() != null
+                    && account.getRecipientStore().needsPniSignature(recipientId);
             try {
                 return s.send(messageSender,
                         address,
diff --git a/lib/src/main/java/org/asamk/signal/manager/internal/MultiAccountManagerImpl.java b/lib/src/main/java/org/asamk/signal/manager/internal/MultiAccountManagerImpl.java
index 560fe62c..0d6a60a8 100644
--- a/lib/src/main/java/org/asamk/signal/manager/internal/MultiAccountManagerImpl.java
+++ b/lib/src/main/java/org/asamk/signal/manager/internal/MultiAccountManagerImpl.java
@@ -121,7 +121,7 @@ public class MultiAccountManagerImpl implements MultiAccountManager {
             } else {
                 // Phone number — check already loaded managers
                 var existing = managers.stream()
-                        .filter(m -> m.getSelfNumber().equals(identifier))
+                        .filter(m -> identifier.equals(m.getSelfNumber()))
                         .findFirst()
                         .orElse(null);
                 if (existing != null) {
diff --git a/lib/src/main/java/org/asamk/signal/manager/internal/ProvisioningManagerImpl.java b/lib/src/main/java/org/asamk/signal/manager/internal/ProvisioningManagerImpl.java
index 65da23e5..a748611c 100644
--- a/lib/src/main/java/org/asamk/signal/manager/internal/ProvisioningManagerImpl.java
+++ b/lib/src/main/java/org/asamk/signal/manager/internal/ProvisioningManagerImpl.java
@@ -20,7 +20,6 @@ import org.asamk.signal.manager.Manager;
 import org.asamk.signal.manager.ProvisioningManager;
 import org.asamk.signal.manager.Settings;
 import org.asamk.signal.manager.api.UserAlreadyExistsException;
-import org.asamk.signal.manager.config.ServiceConfig;
 import org.asamk.signal.manager.config.ServiceEnvironmentConfig;
 import org.asamk.signal.manager.storage.SignalAccount;
 import org.asamk.signal.manager.storage.accounts.AccountsStore;
@@ -30,17 +29,18 @@ import org.signal.core.models.ServiceId.ACI;
 import org.signal.core.models.ServiceId.PNI;
 import org.signal.core.models.backup.MediaRootBackupKey;
 import org.signal.core.util.crypto.DeviceNameCipher;
+import org.signal.libsignal.net.RequestResult;
 import org.signal.libsignal.protocol.IdentityKey;
 import org.signal.libsignal.protocol.IdentityKeyPair;
 import org.signal.libsignal.protocol.ecc.ECPrivateKey;
 import org.signal.libsignal.zkgroup.profiles.ProfileKey;
+import org.signal.network.api.RegistrationApiV2;
+import org.signal.network.rest.SignalRestClient;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
-import org.whispersystems.signalservice.api.SignalServiceAccountManager;
-import org.whispersystems.signalservice.api.account.DeviceAttributes;
+import org.whispersystems.signalservice.api.account.PreKeyCollection;
 import org.whispersystems.signalservice.api.provisioning.ProvisioningSocket;
 import org.whispersystems.signalservice.api.push.ServiceIdType;
-import org.whispersystems.signalservice.api.push.SignalServiceAddress;
 import org.whispersystems.signalservice.api.push.exceptions.AuthorizationFailedException;
 import org.whispersystems.signalservice.internal.crypto.SecondaryProvisioningCipher;
 import org.whispersystems.signalservice.internal.push.ProvisionMessage;
@@ -68,6 +68,7 @@ import kotlinx.coroutines.CoroutineScope;
 
 import static org.asamk.signal.manager.util.KeyUtils.generatePreKeysForType;
 import static org.asamk.signal.manager.util.Utils.handleResponseException;
+import static org.asamk.signal.manager.util.Utils.runSuspendBlocking;
 
 public class ProvisioningManagerImpl implements ProvisioningManager, Closeable {
 
@@ -114,7 +115,8 @@ public class ProvisioningManagerImpl implements ProvisioningManager, Closeable {
     public URI getDeviceLinkUri() throws TimeoutException, IOException {
         try {
             var url = urlFuture.get(30, TimeUnit.SECONDS);
-            return new URI(url);
+            // Mode.Link(false) does not advertise any capabilities itself.
+            return new URI(url + "&capabilities=nopni");
         } catch (java.util.concurrent.TimeoutException e) {
             throw new TimeoutException("Timed out waiting for provisioning URL");
         } catch (InterruptedException e) {
@@ -148,18 +150,19 @@ public class ProvisioningManagerImpl implements ProvisioningManager, Closeable {
 
         var number = msg.number;
         var aci = ACI.parseOrThrow(msg.aci, msg.aciBinary);
-        var pni = PNI.parseOrThrow(msg.pni, msg.pniBinary);
+        var pni = parsePni(msg);
+        var identifier = number != null ? number : aci.toString();
 
-        logger.info("Received link information from {}, linking in progress ...", number);
+        logger.info("Received link information from {}, linking in progress ...", identifier);
 
         var accountPath = accountsStore.getPathByAci(aci);
-        if (accountPath == null) {
+        if (accountPath == null && number != null) {
             accountPath = accountsStore.getPathByNumber(number);
         }
         final var accountExists = accountPath != null && SignalAccount.accountFileExists(pathConfig.dataPath(),
                 accountPath);
         if (accountExists && !canRelinkExistingAccount(accountPath)) {
-            throw new UserAlreadyExistsException(number, SignalAccount.getFileName(pathConfig.dataPath(), accountPath));
+            throw new UserAlreadyExistsException(identifier, SignalAccount.getFileName(pathConfig.dataPath(), accountPath));
         }
         if (accountPath == null) {
             accountPath = accountsStore.addAccount(number, aci);
@@ -173,7 +176,9 @@ public class ProvisioningManagerImpl implements ProvisioningManager, Closeable {
         try {
             aciIdentity = new IdentityKeyPair(new IdentityKey(msg.aciIdentityKeyPublic.toByteArray()),
                     new ECPrivateKey(msg.aciIdentityKeyPrivate.toByteArray()));
-            pniIdentity = new IdentityKeyPair(new IdentityKey(msg.pniIdentityKeyPublic.toByteArray()),
+            pniIdentity = pni == null
+                    ? null
+                    : new IdentityKeyPair(new IdentityKey(msg.pniIdentityKeyPublic.toByteArray()),
                     new ECPrivateKey(msg.pniIdentityKeyPrivate.toByteArray()));
             profileKey = msg.profileKey == null
                     ? KeyUtils.createProfileKey()
@@ -222,28 +227,14 @@ public class ProvisioningManagerImpl implements ProvisioningManager, Closeable {
             }
 
             final var aciPreKeys = generatePreKeysForType(account.getAccountData(ServiceIdType.ACI));
-            final var pniPreKeys = generatePreKeysForType(account.getAccountData(ServiceIdType.PNI));
+            final var pniPreKeys = pni == null
+                    ? null
+                    : generatePreKeysForType(account.getAccountData(ServiceIdType.PNI));
 
             logger.debug("Finishing new device registration");
-            final var attrs = account.getAccountAttributes(null);
-            final var deviceAttributes = new DeviceAttributes(attrs.getFetchesMessages(),
-                    attrs.getRegistrationId(),
-                    attrs.getPniRegistrationId(),
-                    attrs.getName(),
-                    attrs.getCapabilities());
-            final var unauthAccountManager = SignalServiceAccountManager.createWithStaticCredentials(
-                    serviceEnvironmentConfig.signalServiceConfiguration(),
-                    null,
-                    null,
-                    number,
-                    SignalServiceAddress.DEFAULT_DEVICE_ID,
-                    password,
-                    userAgent,
-                    ServiceConfig.AUTOMATIC_NETWORK_RETRY,
-                    ServiceConfig.GROUP_MAX_SIZE);
-            final var registerResponse = handleResponseException(unauthAccountManager.getRegistrationApi()
-                    .registerAsSecondaryDevice(msg.provisioningCode, deviceAttributes, aciPreKeys, pniPreKeys, null));
-            final var deviceId = Integer.parseInt(registerResponse.getDeviceId());
+            final var registrationApi = new RegistrationApiV2(new SignalRestClient(
+                    serviceEnvironmentConfig.signalServiceConfiguration(), userAgent), false);
+            final var deviceId = registerLinkedDevice(registrationApi, account, msg.provisioningCode, aciPreKeys, pniPreKeys);
 
             account.finishLinking(deviceId, aciPreKeys, pniPreKeys);
             linkingFinished = true;
@@ -277,7 +268,7 @@ public class ProvisioningManagerImpl implements ProvisioningManager, Closeable {
                     newManagerListener.accept(m);
                     m = null;
                 }
-                return number;
+                return identifier;
             } finally {
                 if (m != null) {
                     m.close();
@@ -296,6 +287,71 @@ public class ProvisioningManagerImpl implements ProvisioningManager, Closeable {
         }
     }
 
+    static PNI parsePni(final ProvisionMessage message) throws IOException {
+        if (message.number != null) {
+            return PNI.parseOrThrow(message.pni, message.pniBinary);
+        }
+        if (message.pni != null || message.pniBinary != null
+                || message.pniIdentityKeyPublic != null || message.pniIdentityKeyPrivate != null) {
+            throw new IOException("Provisioning message has PNI material without a phone number");
+        }
+        if (message.authCredentialSalt == null || message.authCredentialSalt.size() == 0) {
+            throw new IOException("Numberless provisioning message is missing the group auth credential salt");
+        }
+        return null;
+    }
+
+    static int registerLinkedDevice(
+            final RegistrationApiV2 registrationApi,
+            final SignalAccount account,
+            final String provisioningCode,
+            final PreKeyCollection aciPreKeys,
+            final PreKeyCollection pniPreKeys
+    ) throws IOException {
+        final var attrs = account.getAccountAttributesV2();
+        final var deviceAttributes = new RegistrationApiV2.DeviceAttributes(attrs.getFetchesMessages(),
+                attrs.getRegistrationId(),
+                attrs.getPniRegistrationId(),
+                attrs.getName(),
+                attrs.getCapabilities());
+        final RequestResult<RegistrationApiV2.LinkDeviceResponse, ? extends RegistrationApiV2.RegisterAsLinkedDeviceError> result =
+                runSuspendBlocking(cont -> registrationApi.registerAsSecondaryDevice(account.getAci(),
+                        account.getPassword(),
+                        provisioningCode,
+                        deviceAttributes,
+                        toRegistrationPreKeys(aciPreKeys),
+                        toRegistrationPreKeys(pniPreKeys),
+                        null,
+                        cont));
+        return getLinkedDeviceId(result);
+    }
+
+    static int getLinkedDeviceId(
+            final RequestResult<RegistrationApiV2.LinkDeviceResponse, ? extends RegistrationApiV2.RegisterAsLinkedDeviceError> result
+    ) throws IOException {
+        if (result instanceof RequestResult.NonSuccess<?> failure) {
+            throw switch (failure.getError()) {
+                case RegistrationApiV2.RegisterAsLinkedDeviceError.IncorrectVerification ignored ->
+                        new AuthorizationFailedException(403, "Device verification failed");
+                case RegistrationApiV2.RegisterAsLinkedDeviceError.MissingCapability ignored ->
+                        new IOException("Linked device is missing a required account capability");
+                case RegistrationApiV2.RegisterAsLinkedDeviceError.MaxLinkedDevices ignored ->
+                        new IOException("Account has reached its linked device limit");
+                case RegistrationApiV2.RegisterAsLinkedDeviceError.InvalidRequest ignored ->
+                        new IOException("Signal rejected the device linking request");
+                case RegistrationApiV2.RegisterAsLinkedDeviceError.RateLimited ignored ->
+                        new IOException("Device linking rate limited; try again later");
+                default -> new IOException("Unexpected device linking response");
+            };
+        }
+        return handleResponseException(result).getDeviceId();
+    }
+
+    static RegistrationApiV2.PreKeyCollection toRegistrationPreKeys(final PreKeyCollection preKeys) {
+        return preKeys == null ? null : new RegistrationApiV2.PreKeyCollection(preKeys.getIdentityKey(),
+                preKeys.getSignedPreKey(), preKeys.getLastResortKyberPreKey());
+    }
+
     @Override
     public void close() throws IOException {
         socketHandle.close();
diff --git a/lib/src/main/java/org/asamk/signal/manager/storage/SignalAccount.java b/lib/src/main/java/org/asamk/signal/manager/storage/SignalAccount.java
index 77511d6e..09a0caa9 100644
--- a/lib/src/main/java/org/asamk/signal/manager/storage/SignalAccount.java
+++ b/lib/src/main/java/org/asamk/signal/manager/storage/SignalAccount.java
@@ -71,6 +71,7 @@ import org.signal.libsignal.protocol.state.SignedPreKeyRecord;
 import org.signal.libsignal.protocol.util.KeyHelper;
 import org.signal.libsignal.zkgroup.InvalidInputException;
 import org.signal.libsignal.zkgroup.profiles.ProfileKey;
+import org.signal.network.api.RegistrationApiV2;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 import org.whispersystems.signalservice.api.SignalServiceAccountDataStore;
@@ -350,7 +351,9 @@ public class SignalAccount implements Closeable {
         this.registered = true;
         this.deviceId = deviceId;
         setPreKeys(ServiceIdType.ACI, aciPreKeys);
-        setPreKeys(ServiceIdType.PNI, pniPreKeys);
+        if (pniPreKeys != null) {
+            setPreKeys(ServiceIdType.PNI, pniPreKeys);
+        }
         save();
     }
 
@@ -1426,6 +1429,29 @@ public class SignalAccount implements Closeable {
         return getCapabilities(isPrimaryDevice());
     }
 
+    public RegistrationApiV2.AccountAttributes getAccountAttributesV2() {
+        final var attributes = getAccountAttributes(null);
+        final var capabilities = attributes.getCapabilities();
+        return new RegistrationApiV2.AccountAttributes(attributes.getSignalingKey(),
+                attributes.getRegistrationId(),
+                attributes.getVoice(),
+                attributes.getVideo(),
+                attributes.getFetchesMessages(),
+                attributes.getRegistrationLock(),
+                attributes.getUnidentifiedAccessKey(),
+                attributes.getUnrestrictedUnidentifiedAccess(),
+                number == null ? null : attributes.getDiscoverableByPhoneNumber(),
+                new RegistrationApiV2.AccountAttributes.Capabilities(capabilities.getStorage(),
+                        capabilities.getVersionedExpirationTimer(),
+                        capabilities.getAttachmentBackfill(),
+                        capabilities.getSpqr(),
+                        capabilities.getUsernameChangeSyncMessage(),
+                        capabilities.getOptionalPhoneNumber()),
+                attributes.getName(),
+                getPni() == null ? null : attributes.getPniRegistrationId(),
+                attributes.getRecoveryPassword());
+    }
+
     public ServiceId getAccountId(ServiceIdType serviceIdType) {
         return getAccountData(serviceIdType).getServiceId();
     }
diff --git a/lib/src/main/java/org/asamk/signal/manager/storage/accounts/AccountsStore.java b/lib/src/main/java/org/asamk/signal/manager/storage/accounts/AccountsStore.java
index 36a6c75e..e9f27384 100644
--- a/lib/src/main/java/org/asamk/signal/manager/storage/accounts/AccountsStore.java
+++ b/lib/src/main/java/org/asamk/signal/manager/storage/accounts/AccountsStore.java
@@ -63,11 +63,14 @@ public class AccountsStore {
     public synchronized Set<AccountsStorage.Account> getAllAccounts() throws IOException {
         return readAccounts().stream()
                 .filter(a -> a.environment() == null || serviceEnvironment.equals(a.environment()))
-                .filter(a -> a.number() != null)
+                .filter(a -> a.number() != null || a.uuid() != null)
                 .collect(Collectors.toSet());
     }
 
     public synchronized String getPathByNumber(String number) throws IOException {
+        if (number == null) {
+            return null;
+        }
         return readAccounts().stream()
                 .filter(a -> a.environment() == null || serviceEnvironment.equals(a.environment()))
                 .filter(a -> number.equals(a.number()))
@@ -101,7 +104,7 @@ public class AccountsStore {
             if (number != null && number.equals(a.number())) {
                 return new AccountsStorage.Account(a.path(), a.environment(), null, a.uuid());
             }
-            if (aci != null && aci.toString().equals(a.toString())) {
+            if (aci != null && aci.toString().equals(a.uuid())) {
                 return new AccountsStorage.Account(a.path(), a.environment(), a.number(), null);
             }
 
diff --git a/lib/src/main/java/org/asamk/signal/manager/util/PhoneNumberFormatter.java b/lib/src/main/java/org/asamk/signal/manager/util/PhoneNumberFormatter.java
index cc0c6503..d96bb457 100644
--- a/lib/src/main/java/org/asamk/signal/manager/util/PhoneNumberFormatter.java
+++ b/lib/src/main/java/org/asamk/signal/manager/util/PhoneNumberFormatter.java
@@ -42,6 +42,18 @@ public class PhoneNumberFormatter {
             throw new InvalidNumberException("No valid characters found.");
         }
 
+        if (localNumber == null) {
+            if (!number.startsWith("+")) {
+                throw new InvalidNumberException("Use an international number including the country code for a numberless account.");
+            }
+            try {
+                final var util = PhoneNumberUtil.getInstance();
+                return util.format(util.parse(number, null), PhoneNumberFormat.E164);
+            } catch (NumberParseException e) {
+                throw new InvalidNumberException("Invalid international phone number.");
+            }
+        }
+
         try {
             PhoneNumberUtil util = PhoneNumberUtil.getInstance();
             PhoneNumber localNumberObject = util.parse(localNumber, null);
diff --git a/lib/src/test/java/org/asamk/signal/manager/helper/NumberlessGroupTest.java b/lib/src/test/java/org/asamk/signal/manager/helper/NumberlessGroupTest.java
new file mode 100644
index 00000000..8bf8a0cd
--- /dev/null
+++ b/lib/src/test/java/org/asamk/signal/manager/helper/NumberlessGroupTest.java
@@ -0,0 +1,41 @@
+package org.asamk.signal.manager.helper;
+
+import org.asamk.signal.manager.Settings;
+import org.asamk.signal.manager.api.ServiceEnvironment;
+import org.asamk.signal.manager.storage.SignalAccount;
+import org.asamk.signal.manager.util.KeyUtils;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.io.TempDir;
+import org.signal.core.models.ServiceId.ACI;
+import org.signal.storageservice.storage.protos.groups.local.DecryptedGroup;
+import org.signal.storageservice.storage.protos.groups.local.DecryptedMember;
+
+import java.nio.file.Path;
+import java.util.List;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+class NumberlessGroupTest {
+
+    @TempDir
+    Path directory;
+
+    @Test
+    void findsOurGroupMembershipByAciWhenPniIsAbsent() throws Exception {
+        final var aci = ACI.parseOrThrow("11111111-1111-4111-8111-111111111111");
+        final var otherAci = ACI.parseOrThrow("22222222-2222-4222-8222-222222222222");
+        try (final var account = SignalAccount.createLinkedAccount(directory.toFile(), "account",
+                ServiceEnvironment.STAGING, Settings.DEFAULT);
+             final var context = new Context(account, null, null, null, null, null)) {
+            account.setProvisioningData(null, aci, null, "test-password", new byte[]{1},
+                    KeyUtils.generateIdentityKeyPair(), null, KeyUtils.createProfileKey(), null, new byte[32], null);
+            final var otherMember = new DecryptedMember.Builder().aciBytes(otherAci.toByteString())
+                    .joinedAtRevision(1).build();
+            final var selfMember = new DecryptedMember.Builder().aciBytes(aci.toByteString())
+                    .joinedAtRevision(4).build();
+            final var group = new DecryptedGroup.Builder().revision(9).members(List.of(otherMember, selfMember)).build();
+            assertEquals(4, context.getGroupV2Helper().findRevisionWeWereAdded(group));
+            assertEquals(9, context.getGroupV2Helper().findRevisionWeWereAdded(group.newBuilder().members(List.of(otherMember)).build()));
+        }
+    }
+}
diff --git a/lib/src/test/java/org/asamk/signal/manager/internal/NumberlessProvisioningTest.java b/lib/src/test/java/org/asamk/signal/manager/internal/NumberlessProvisioningTest.java
new file mode 100644
index 00000000..c3ad6d71
--- /dev/null
+++ b/lib/src/test/java/org/asamk/signal/manager/internal/NumberlessProvisioningTest.java
@@ -0,0 +1,131 @@
+package org.asamk.signal.manager.internal;
+
+import com.fasterxml.jackson.databind.JsonNode;
+import com.fasterxml.jackson.databind.ObjectMapper;
+
+import org.asamk.signal.manager.Settings;
+import org.asamk.signal.manager.api.ServiceEnvironment;
+import org.asamk.signal.manager.config.ServiceConfig;
+import org.asamk.signal.manager.storage.SignalAccount;
+import org.asamk.signal.manager.util.KeyUtils;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.io.TempDir;
+import org.signal.core.models.ServiceId.ACI;
+import org.signal.core.models.ServiceId.PNI;
+import org.signal.libsignal.net.RequestResult;
+import org.signal.network.api.RegistrationApiV2;
+import org.signal.network.rest.SignalRestClient;
+import org.whispersystems.signalservice.api.push.ServiceIdType;
+import org.whispersystems.signalservice.api.push.exceptions.AuthorizationFailedException;
+import org.whispersystems.signalservice.internal.push.ProvisionMessage;
+
+import java.io.IOException;
+import java.nio.file.Path;
+import java.security.SecureRandom;
+import java.util.concurrent.atomic.AtomicReference;
+
+import okhttp3.MediaType;
+import okhttp3.OkHttpClient;
+import okhttp3.Protocol;
+import okhttp3.Request;
+import okhttp3.Response;
+import okhttp3.ResponseBody;
+import okio.Buffer;
+import okio.ByteString;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+class NumberlessProvisioningTest {
+
+    private static final ACI ACI_ID = ACI.parseOrThrow("11111111-1111-4111-8111-111111111111");
+    private static final PNI PNI_ID = PNI.parseOrThrow("22222222-2222-4222-8222-222222222222");
+
+    @TempDir
+    Path directory;
+
+    @Test
+    void numberlessProvisioningRequiresGroupCredentialSalt() {
+        assertThrows(IOException.class, () -> ProvisioningManagerImpl.parsePni(new ProvisionMessage.Builder().build()));
+        assertThrows(IOException.class, () -> ProvisioningManagerImpl.parsePni(new ProvisionMessage.Builder()
+                .authCredentialSalt(ByteString.EMPTY).build()));
+        assertNull(ProvisioningManagerImpl.toRegistrationPreKeys(null));
+    }
+
+    @Test
+    void acceptsNumberlessProvisioningButRejectsInconsistentPhoneIdentity() throws Exception {
+        final var message = new ProvisionMessage.Builder().authCredentialSalt(ByteString.of(new byte[32]));
+        assertNull(ProvisioningManagerImpl.parsePni(message.build()));
+        assertThrows(IOException.class, () -> ProvisioningManagerImpl.parsePni(message.pni(PNI_ID.toString()).build()));
+        assertThrows(IllegalArgumentException.class, () -> ProvisioningManagerImpl.parsePni(
+                new ProvisionMessage.Builder().number("+12025550123").build()));
+        assertEquals(PNI_ID, ProvisioningManagerImpl.parsePni(new ProvisionMessage.Builder()
+                .number("+12025550123").pni(PNI_ID.toString()).build()));
+    }
+
+    @Test
+    void numberlessLinkRequestOmitsPniAndAuthenticatesWithAci() throws Exception {
+        checkLinkRequest(null, null);
+    }
+
+    @Test
+    void numberedLinkRequestStillIncludesPniKeys() throws Exception {
+        checkLinkRequest("+12025550123", PNI_ID);
+    }
+
+    private void checkLinkRequest(final String number, final PNI pni) throws Exception {
+        final var request = new AtomicReference<Request>();
+        final var body = new AtomicReference<JsonNode>();
+        final var mapper = new ObjectMapper();
+        final var client = new OkHttpClient.Builder().addInterceptor(chain -> {
+            request.set(chain.request());
+            final var buffer = new Buffer();
+            chain.request().body().writeTo(buffer);
+            body.set(mapper.readTree(buffer.readUtf8()));
+            return new Response.Builder().request(chain.request()).protocol(Protocol.HTTP_1_1)
+                    .code(200).message("OK")
+                    .body(ResponseBody.create("{\"deviceId\":2}", MediaType.get("application/json"))).build();
+        }).build();
+        final var config = ServiceConfig.getServiceEnvironmentConfig(ServiceEnvironment.STAGING, "signal-cli-test");
+        final var restClient = new SignalRestClient(config.signalServiceConfiguration(), "signal-cli-test",
+                null, false, 1000L, new SecureRandom(), client);
+        final var api = new RegistrationApiV2(restClient, false);
+
+        try (final var account = SignalAccount.createLinkedAccount(directory.toFile(), "account",
+                ServiceEnvironment.STAGING, Settings.DEFAULT)) {
+            account.setProvisioningData(number, ACI_ID, pni, "test-password", new byte[]{1},
+                    KeyUtils.generateIdentityKeyPair(), pni == null ? null : KeyUtils.generateIdentityKeyPair(),
+                    KeyUtils.createProfileKey(), null, new byte[32], null);
+            final var aciKeys = KeyUtils.generatePreKeysForType(account.getAccountData(ServiceIdType.ACI));
+            final var pniKeys = pni == null ? null : KeyUtils.generatePreKeysForType(account.getAccountData(ServiceIdType.PNI));
+            final var deviceId = ProvisioningManagerImpl.registerLinkedDevice(api, account, "test-code", aciKeys, pniKeys);
+
+            assertEquals(2, deviceId);
+            assertEquals("PUT", request.get().method());
+            assertEquals("/v1/devices/link", request.get().url().encodedPath());
+            assertEquals(okhttp3.Credentials.basic(ACI_ID.toString(), "test-password"), request.get().header("Authorization"));
+            assertTrue(body.get().path("accountAttributes").path("capabilities").path("optionalPhoneNumber").asBoolean());
+            assertTrue(body.get().hasNonNull("aciSignedPreKey"));
+            assertTrue(body.get().hasNonNull("aciPqLastResortPreKey"));
+            assertEquals(pni != null, body.get().has("pniSignedPreKey"));
+            assertEquals(pni != null, body.get().has("pniPqLastResortPreKey"));
+            assertEquals(pni != null, body.get().path("accountAttributes").has("pniRegistrationId"));
+        } finally {
+            client.dispatcher().executorService().shutdown();
+            client.connectionPool().evictAll();
+        }
+    }
+
+    @Test
+    @SuppressWarnings("unchecked")
+    void linkingErrorsAreReportedWithoutCrashingOrIncludingServerBody() {
+        assertThrows(AuthorizationFailedException.class, () -> ProvisioningManagerImpl.getLinkedDeviceId(
+                new RequestResult.NonSuccess<>(RegistrationApiV2.RegisterAsLinkedDeviceError.IncorrectVerification.INSTANCE)));
+        final var error = assertThrows(IOException.class, () -> ProvisioningManagerImpl.getLinkedDeviceId(
+                new RequestResult.NonSuccess<>(new RegistrationApiV2.RegisterAsLinkedDeviceError.InvalidRequest("secret payload"))));
+        assertFalse(error.getMessage().contains("secret payload"));
+    }
+}
diff --git a/lib/src/test/java/org/asamk/signal/manager/storage/NumberlessAccountTest.java b/lib/src/test/java/org/asamk/signal/manager/storage/NumberlessAccountTest.java
new file mode 100644
index 00000000..5e8f54be
--- /dev/null
+++ b/lib/src/test/java/org/asamk/signal/manager/storage/NumberlessAccountTest.java
@@ -0,0 +1,53 @@
+package org.asamk.signal.manager.storage;
+
+import org.asamk.signal.manager.Settings;
+import org.asamk.signal.manager.api.ServiceEnvironment;
+import org.asamk.signal.manager.util.KeyUtils;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.io.TempDir;
+import org.signal.core.models.ServiceId.ACI;
+import org.whispersystems.signalservice.api.push.ServiceIdType;
+
+import java.nio.file.Path;
+
+import static org.junit.jupiter.api.Assertions.assertArrayEquals;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+class NumberlessAccountTest {
+
+    @TempDir
+    Path directory;
+
+    @Test
+    void numberlessLinkedAccountSurvivesReload() throws Exception {
+        final var aci = ACI.parseOrThrow("11111111-1111-4111-8111-111111111111");
+        final var identity = KeyUtils.generateIdentityKeyPair();
+        final var salt = new byte[32];
+        salt[0] = 42;
+        try (final var account = SignalAccount.createLinkedAccount(directory.toFile(), "account",
+                ServiceEnvironment.STAGING, Settings.DEFAULT)) {
+            account.setProvisioningData(null, aci, null, "test-password", new byte[]{1}, identity,
+                    null, KeyUtils.createProfileKey(), null, salt, null);
+            account.finishLinking(2, KeyUtils.generatePreKeysForType(account.getAccountData(ServiceIdType.ACI)), null);
+        }
+
+        try (final var account = SignalAccount.load(directory.toFile(), "account", true, Settings.DEFAULT)) {
+            assertTrue(account.isRegistered());
+            assertFalse(account.isPrimaryDevice());
+            assertEquals(2, account.getDeviceId());
+            assertEquals(aci, account.getAci());
+            assertNull(account.getNumber());
+            assertNull(account.getPni());
+            assertNull(account.getPniIdentityKeyPair());
+            assertNull(account.getSignalServiceDataStore().pniOrNull());
+            assertArrayEquals(identity.serialize(), account.getAciIdentityKeyPair().serialize());
+            assertArrayEquals(salt, account.getAuthCredentialSalt());
+            assertNull(account.getAccountAttributesV2().getPniRegistrationId());
+            assertNull(account.getAccountAttributesV2().getDiscoverableByPhoneNumber());
+            assertTrue(account.getAccountAttributesV2().getCapabilities().getOptionalPhoneNumber());
+        }
+    }
+}
diff --git a/lib/src/test/java/org/asamk/signal/manager/storage/accounts/AccountsStoreTest.java b/lib/src/test/java/org/asamk/signal/manager/storage/accounts/AccountsStoreTest.java
new file mode 100644
index 00000000..32d032d7
--- /dev/null
+++ b/lib/src/test/java/org/asamk/signal/manager/storage/accounts/AccountsStoreTest.java
@@ -0,0 +1,47 @@
+package org.asamk.signal.manager.storage.accounts;
+
+import org.asamk.signal.manager.api.ServiceEnvironment;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.io.TempDir;
+import org.signal.core.models.ServiceId.ACI;
+
+import java.nio.file.Path;
+import java.util.Set;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+class AccountsStoreTest {
+
+    @TempDir
+    Path directory;
+
+    @Test
+    void discoversNumberlessAccountsByAciAndKeepsEnvironmentsSeparate() throws Exception {
+        final var store = new AccountsStore(directory.toFile(), ServiceEnvironment.STAGING, path -> null);
+        final var aci = ACI.parseOrThrow("11111111-1111-4111-8111-111111111111");
+        final var path = store.addAccount(null, aci);
+        store.addAccount("+12025550123", null);
+
+        final var reopened = new AccountsStore(directory.toFile(), ServiceEnvironment.STAGING, ignored -> null);
+        assertEquals(2, reopened.getAllAccounts().size());
+        assertEquals(path, reopened.getPathByAci(aci));
+        assertNull(reopened.getPathByNumber(null));
+        assertEquals(Set.of("+12025550123"), reopened.getAllNumbers());
+        assertTrue(new AccountsStore(directory.toFile(), ServiceEnvironment.LIVE, ignored -> null).getAllAccounts().isEmpty());
+    }
+
+    @Test
+    void updatingAnAciDoesNotLeaveDuplicateNumberlessAccounts() throws Exception {
+        final var store = new AccountsStore(directory.toFile(), ServiceEnvironment.STAGING, path -> null);
+        final var aci = ACI.parseOrThrow("11111111-1111-4111-8111-111111111111");
+        final var oldPath = store.addAccount(null, aci);
+        java.nio.file.Files.createFile(directory.resolve(oldPath));
+        final var newPath = store.addAccount(null, null);
+        store.updateAccount(newPath, null, aci);
+
+        assertEquals(newPath, store.getPathByAci(aci));
+        assertEquals(1, store.getAllAccounts().size());
+    }
+}
diff --git a/lib/src/test/java/org/asamk/signal/manager/util/PhoneNumberFormatterTest.java b/lib/src/test/java/org/asamk/signal/manager/util/PhoneNumberFormatterTest.java
new file mode 100644
index 00000000..5da9932b
--- /dev/null
+++ b/lib/src/test/java/org/asamk/signal/manager/util/PhoneNumberFormatterTest.java
@@ -0,0 +1,25 @@
+package org.asamk.signal.manager.util;
+
+import org.asamk.signal.manager.api.InvalidNumberException;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+class PhoneNumberFormatterTest {
+
+    @Test
+    void numberlessAccountsCanAddressInternationalPhoneNumbers() throws Exception {
+        assertEquals("+12025550123", PhoneNumberFormatter.formatNumber("+1 (202) 555-0123", null));
+    }
+
+    @Test
+    void numberlessAccountsCannotInferACountryCode() {
+        assertThrows(InvalidNumberException.class, () -> PhoneNumberFormatter.formatNumber("2025550123", null));
+    }
+
+    @Test
+    void numberedAccountsStillInferTheirCountryCode() throws Exception {
+        assertEquals("+12025550123", PhoneNumberFormatter.formatNumber("2025550123", "+12025550124"));
+    }
+}
diff --git a/man/signal-cli-jsonrpc.5.adoc b/man/signal-cli-jsonrpc.5.adoc
index b9abb8ce..b9162925 100644
--- a/man/signal-cli-jsonrpc.5.adoc
+++ b/man/signal-cli-jsonrpc.5.adoc
@@ -76,6 +76,9 @@ Messages are then sent similar to the automatic mode, but wrapped in a subscript
 When the daemon/jsonRpc command is started without an account parameter (-a), signal-cli will provide all local accounts and additional commands to register (`register`) and link (`startLink`, `finishLink`) new accounts.
 
 In multi-account mode, requests for a single account require an additional `account` param.
+For an account without a phone number, this parameter must be its ACI (Account ID).
+`listAccounts` returns the ACI in `aci` and a null `number` for these accounts.
+Receive events identify them by ACI in the `account` field.
 
 REQUEST: `{"jsonrpc":"2.0","method":"listGroups","id":"my special mark","params":{"account":"+33123456789"}}`
 
@@ -132,7 +135,10 @@ Params:
 
 REQUEST: `{"jsonrpc":"2.0","method":"finishLink","id":"6","params":{"deviceLinkUri":"sgnl://linkdevice?uuid=X&pub_key=X","deviceName":"new-name"}}`
 
-RESPONSE: `{"jsonrpc":"2.0","result":{"deviceLinkUri":"sgnl://linkdevice?uuid=X&pub_key=X"},"id":"6"}`
+RESPONSE: `{"jsonrpc":"2.0","result":{"number":null,"aci":"11111111-1111-4111-8111-111111111111"},"id":"6"}`
+
+The `number` field contains the phone number for a numbered account. Linking a numberless
+account uses the same QR flow; no Account Key is supplied to `finishLink`.
 
 == Examples
 
diff --git a/man/signal-cli.1.adoc b/man/signal-cli.1.adoc
index 26fac479..fed04403 100644
--- a/man/signal-cli.1.adoc
+++ b/man/signal-cli.1.adoc
@@ -65,6 +65,7 @@ Make sure you have full read/write access to the given directory.
 *-a* ACCOUNT, *--account* ACCOUNT::
 Specify your phone number, that will be your identifier.
 The phone number must include the country calling code, i.e. the number must start with a "+" sign.
+An ACI (Account ID) can also select an existing account and is required for an account without a phone number.
 
 This flag must not be given for the `link` command.
 It is optional for the `daemon` command.
diff --git a/src/main/java/org/asamk/signal/App.java b/src/main/java/org/asamk/signal/App.java
index fa18e597..be8aab1b 100644
--- a/src/main/java/org/asamk/signal/App.java
+++ b/src/main/java/org/asamk/signal/App.java
@@ -208,14 +208,14 @@ public class App {
     private static String getAccountIfOnlyOne(final SignalAccountFiles signalAccountFiles) throws IOErrorException, UserErrorException {
         Set<String> accounts;
         try {
-            accounts = signalAccountFiles.getAllLocalAccountNumbers();
+            accounts = signalAccountFiles.getAllLocalAccountIdentifiers();
         } catch (IOException e) {
             throw new IOErrorException("Failed to load local accounts file", e);
         }
         if (accounts.isEmpty()) {
             throw new UserErrorException("No local users found, you first need to register or link an account");
         } else if (accounts.size() > 1) {
-            throw new UserErrorException("Multiple users found, you need to specify an account (phone number) with -a");
+            throw new UserErrorException("Multiple users found, you need to specify an account (phone number or ACI) with -a");
         }
         return accounts.stream().findFirst().get();
     }
diff --git a/src/main/java/org/asamk/signal/ReceiveMessageHandler.java b/src/main/java/org/asamk/signal/ReceiveMessageHandler.java
index d179aed0..e3127a67 100644
--- a/src/main/java/org/asamk/signal/ReceiveMessageHandler.java
+++ b/src/main/java/org/asamk/signal/ReceiveMessageHandler.java
@@ -39,7 +39,7 @@ public class ReceiveMessageHandler implements Manager.ReceiveMessageHandler {
         writer.println("Envelope from: {} (device: {}) to {}",
                 source.map(this::formatContact).orElse("unknown source"),
                 envelope.sourceDevice(),
-                m.getSelfNumber());
+                m.getSelfIdentifier());
         writer.println("Timestamp: {}", DateUtils.formatTimestamp(envelope.timestamp()));
         writer.println("Server timestamps: received: {} delivered: {}",
                 DateUtils.formatTimestamp(envelope.serverReceivedTimestamp()),
@@ -55,13 +55,13 @@ public class ReceiveMessageHandler implements Manager.ReceiveMessageHandler {
                 final var recipientName = e.getSender().getLegacyIdentifier();
                 writer.println(
                         "Use 'signal-cli -a {} listIdentities -n {}', verify the key and run 'signal-cli -a {} trust -v \"FINGER_PRINT\" {}' to mark it as trusted",
-                        m.getSelfNumber(),
+                        m.getSelfIdentifier(),
                         recipientName,
-                        m.getSelfNumber(),
+                        m.getSelfIdentifier(),
                         recipientName);
                 writer.println(
                         "If you don't care about security, use 'signal-cli -a {} trust -a {}' to trust it without verification",
-                        m.getSelfNumber(),
+                        m.getSelfIdentifier(),
                         recipientName);
             } else {
                 writer.println("Exception: {} ({})", exception.getMessage(), exception.getClass().getSimpleName());
diff --git a/src/main/java/org/asamk/signal/commands/FinishLinkCommand.java b/src/main/java/org/asamk/signal/commands/FinishLinkCommand.java
index c9282616..8a8f8454 100644
--- a/src/main/java/org/asamk/signal/commands/FinishLinkCommand.java
+++ b/src/main/java/org/asamk/signal/commands/FinishLinkCommand.java
@@ -54,9 +54,9 @@ public class FinishLinkCommand implements JsonRpcMultiCommand<FinishLinkCommand.
         if (deviceName == null) {
             deviceName = "cli";
         }
-        final String number;
+        final String identifier;
         try {
-            number = provisioningManager.finishDeviceLink(deviceName);
+            identifier = provisioningManager.finishDeviceLink(deviceName);
         } catch (TimeoutException e) {
             throw new UserErrorException("Link request timed out, please try again.");
         } catch (IOException e) {
@@ -73,10 +73,11 @@ public class FinishLinkCommand implements JsonRpcMultiCommand<FinishLinkCommand.
                     + "\" before trying again.");
         }
 
-        jsonWriter.write(new JsonFinishLink(number));
+        final var manager = m.getManager(identifier);
+        jsonWriter.write(new JsonFinishLink(manager.getSelfNumber(), manager.getSelfACI()));
     }
 
     public record FinishLinkParams(String deviceLinkUri, String deviceName) {}
 
-    private record JsonFinishLink(String number) {}
+    private record JsonFinishLink(String number, String aci) {}
 }
diff --git a/src/main/java/org/asamk/signal/commands/ListAccountsCommand.java b/src/main/java/org/asamk/signal/commands/ListAccountsCommand.java
index b9542934..333a4443 100644
--- a/src/main/java/org/asamk/signal/commands/ListAccountsCommand.java
+++ b/src/main/java/org/asamk/signal/commands/ListAccountsCommand.java
@@ -27,19 +27,20 @@ public class ListAccountsCommand implements JsonRpcMultiLocalCommand {
             final MultiAccountManager c,
             final OutputWriter outputWriter
     ) throws CommandException {
-        final var accountNumbers = c.getAccountNumbers();
+        final var managers = c.getManagers();
         switch (outputWriter) {
             case JsonWriter jsonWriter -> {
-                final var jsonAccounts = accountNumbers.stream().map(JsonAccount::new).toList();
+                final var jsonAccounts = managers.stream().map(m -> new JsonAccount(m.getSelfNumber(), m.getSelfACI())).toList();
                 jsonWriter.write(jsonAccounts);
             }
             case PlainTextWriter plainTextWriter -> {
-                for (final var number : accountNumbers) {
-                    plainTextWriter.println("Number: {}", number);
+                for (final var manager : managers) {
+                    plainTextWriter.println(manager.getSelfNumber() != null ? "Number: {}" : "ACI: {}",
+                            manager.getSelfIdentifier());
                 }
             }
         }
     }
 
-    private record JsonAccount(String number) {}
+    private record JsonAccount(String number, String aci) {}
 }
diff --git a/src/main/java/org/asamk/signal/json/JsonReceiveMessageHandler.java b/src/main/java/org/asamk/signal/json/JsonReceiveMessageHandler.java
index ca0dba2b..cb2fa4e1 100644
--- a/src/main/java/org/asamk/signal/json/JsonReceiveMessageHandler.java
+++ b/src/main/java/org/asamk/signal/json/JsonReceiveMessageHandler.java
@@ -23,7 +23,7 @@ public class JsonReceiveMessageHandler implements Manager.ReceiveMessageHandler
     @Override
     public void handleMessage(MessageEnvelope envelope, Throwable exception) {
         final var object = new HashMap<String, Object>();
-        object.put("account", m.getSelfNumber());
+        object.put("account", m.getSelfIdentifier());
         if (exception != null) {
             object.put("exception", JsonError.from(exception));
         }
diff --git a/src/test/java/org/asamk/signal/json/NumberlessAccountOutputTest.java b/src/test/java/org/asamk/signal/json/NumberlessAccountOutputTest.java
new file mode 100644
index 00000000..15a2bd09
--- /dev/null
+++ b/src/test/java/org/asamk/signal/json/NumberlessAccountOutputTest.java
@@ -0,0 +1,70 @@
+package org.asamk.signal.json;
+
+import com.fasterxml.jackson.databind.ObjectMapper;
+
+import org.asamk.signal.commands.ListAccountsCommand;
+import org.asamk.signal.manager.Manager;
+import org.asamk.signal.manager.internal.MultiAccountManagerImpl;
+import org.junit.jupiter.api.Test;
+
+import java.lang.reflect.InvocationHandler;
+import java.lang.reflect.Proxy;
+import java.util.List;
+import java.util.Map;
+import java.util.concurrent.atomic.AtomicReference;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertSame;
+
+class NumberlessAccountOutputTest {
+
+    private static final String ACI = "11111111-1111-4111-8111-111111111111";
+
+    @Test
+    void receiveEventsIdentifyNumberlessAccountByAci() {
+        final var output = new AtomicReference<Object>();
+        new JsonReceiveMessageHandler(manager(null), output::set).handleMessage(null, null);
+        assertEquals(ACI, ((Map<?, ?>) output.get()).get("account"));
+    }
+
+    @Test
+    void receiveEventsKeepNumberedAccountIdentifiers() {
+        final var output = new AtomicReference<Object>();
+        new JsonReceiveMessageHandler(manager("+12025550123"), output::set).handleMessage(null, null);
+        assertEquals("+12025550123", ((Map<?, ?>) output.get()).get("account"));
+    }
+
+    @Test
+    void listAccountsIncludesAciWithoutPuttingItInTheNumberField() throws Exception {
+        final var numberless = manager(null);
+        final var numbered = manager("+12025550123");
+        final var multi = new MultiAccountManagerImpl(List.of(numberless, numbered), null);
+        final var output = new AtomicReference<Object>();
+        new ListAccountsCommand().handleCommand(Map.of(), multi, output::set);
+        final var accounts = new ObjectMapper().valueToTree(output.get());
+        assertEquals(2, accounts.size());
+        for (final var account : accounts) {
+            assertEquals(ACI, account.path("aci").asText());
+            assertFalse(ACI.equals(account.path("number").asText()));
+        }
+        assertSame(numbered, multi.getManager("+12025550123"));
+    }
+
+    private static Manager manager(final String number) {
+        return (Manager) Proxy.newProxyInstance(Manager.class.getClassLoader(), new Class<?>[]{Manager.class},
+                (proxy, method, args) -> {
+                    if (method.isDefault()) {
+                        return InvocationHandler.invokeDefault(proxy, method, args);
+                    }
+                    return switch (method.getName()) {
+                        case "getSelfNumber" -> number;
+                        case "getSelfACI" -> ACI;
+                        case "hashCode" -> System.identityHashCode(proxy);
+                        case "equals" -> proxy == args[0];
+                        case "addClosedListener" -> null;
+                        default -> throw new UnsupportedOperationException(method.getName());
+                    };
+                });
+    }
+}