diff --git a/service/src/main/java/org/whispersystems/textsecuregcm/controllers/VerificationController.java b/service/src/main/java/org/whispersystems/textsecuregcm/controllers/VerificationController.java
index de7897136..087a2b594 100644
--- a/service/src/main/java/org/whispersystems/textsecuregcm/controllers/VerificationController.java
+++ b/service/src/main/java/org/whispersystems/textsecuregcm/controllers/VerificationController.java
@@ -74,6 +74,7 @@ import org.whispersystems.textsecuregcm.registration.MessageTransport;
 import org.whispersystems.textsecuregcm.registration.RegistrationServiceClient;
 import org.whispersystems.textsecuregcm.registration.RegistrationServiceException;
 import org.whispersystems.textsecuregcm.registration.RegistrationServiceSenderException;
+import org.whispersystems.textsecuregcm.registration.TransportNotAllowedException;
 import org.whispersystems.textsecuregcm.registration.VerificationSession;
 import org.whispersystems.textsecuregcm.spam.Extract;
 import org.whispersystems.textsecuregcm.spam.FilterSpam;
@@ -488,8 +489,13 @@ public class VerificationController {
 
         throw registrationServiceException.getRegistrationSession()
             .map(s -> buildResponse(s, verificationSession))
-            .map(verificationSessionResponse -> new ClientErrorException(
-                Response.status(Response.Status.CONFLICT).entity(verificationSessionResponse).build()))
+            .map(verificationSessionResponse -> {
+              final Response response = registrationServiceException instanceof TransportNotAllowedException
+                  ? Response.status(418).entity(verificationSessionResponse).build()
+                  : Response.status(Response.Status.CONFLICT).entity(verificationSessionResponse).build();
+
+              return new ClientErrorException(response);
+            })
             .orElseGet(NotFoundException::new);
 
       } else if (unwrappedException instanceof RegistrationServiceSenderException) {
diff --git a/service/src/main/java/org/whispersystems/textsecuregcm/registration/RegistrationServiceClient.java b/service/src/main/java/org/whispersystems/textsecuregcm/registration/RegistrationServiceClient.java
index d3fcfb330..5e83c7caf 100644
--- a/service/src/main/java/org/whispersystems/textsecuregcm/registration/RegistrationServiceClient.java
+++ b/service/src/main/java/org/whispersystems/textsecuregcm/registration/RegistrationServiceClient.java
@@ -157,6 +157,8 @@ public class RegistrationServiceClient implements Managed {
                   RegistrationServiceSenderException.illegalArgument(response.getError().getMayRetry()));
               case SEND_VERIFICATION_CODE_ERROR_TYPE_UNSPECIFIED -> throw new CompletionException(
                   RegistrationServiceSenderException.unknown(response.getError().getMayRetry()));
+              case SEND_VERIFICATION_CODE_ERROR_TYPE_TRANSPORT_NOT_ALLOWED -> throw new CompletionException(
+                  new TransportNotAllowedException(buildSessionResponseFromMetadata(response.getSessionMetadata())));
 
               default -> throw new CompletionException(
                   new RuntimeException("Failed to send verification code: " + response.getError().getErrorType()));
diff --git a/service/src/main/java/org/whispersystems/textsecuregcm/registration/TransportNotAllowedException.java b/service/src/main/java/org/whispersystems/textsecuregcm/registration/TransportNotAllowedException.java
new file mode 100644
index 000000000..095858ac6
--- /dev/null
+++ b/service/src/main/java/org/whispersystems/textsecuregcm/registration/TransportNotAllowedException.java
@@ -0,0 +1,14 @@
+package org.whispersystems.textsecuregcm.registration;
+
+import org.whispersystems.textsecuregcm.entities.RegistrationServiceSession;
+
+/**
+ * Indicates that a request to send a verification code failed because the destination number does not support the
+ * requested transport (e.g. the caller asked to send an SMS to a landline number).
+ */
+public class TransportNotAllowedException extends RegistrationServiceException {
+
+  public TransportNotAllowedException(RegistrationServiceSession registrationServiceSession) {
+    super(registrationServiceSession);
+  }
+}
diff --git a/service/src/main/proto/RegistrationService.proto b/service/src/main/proto/RegistrationService.proto
index ea3f33ca2..75c6ac3ad 100644
--- a/service/src/main/proto/RegistrationService.proto
+++ b/service/src/main/proto/RegistrationService.proto
@@ -318,6 +318,13 @@ enum SendVerificationCodeErrorType {
    * been verified.
    */
   SEND_VERIFICATION_CODE_ERROR_TYPE_SESSION_ALREADY_VERIFIED = 5;
+
+  /**
+   * A verification code could not be sent via the requested transport because
+   * the destination phone number (or the sender) does not support the requested
+   * transport.
+   */
+  SEND_VERIFICATION_CODE_ERROR_TYPE_TRANSPORT_NOT_ALLOWED = 6;
 }
 
 message CheckVerificationCodeRequest {
diff --git a/service/src/test/java/org/whispersystems/textsecuregcm/controllers/VerificationControllerTest.java b/service/src/test/java/org/whispersystems/textsecuregcm/controllers/VerificationControllerTest.java
index 1b0db7350..ad8fe0838 100644
--- a/service/src/test/java/org/whispersystems/textsecuregcm/controllers/VerificationControllerTest.java
+++ b/service/src/test/java/org/whispersystems/textsecuregcm/controllers/VerificationControllerTest.java
@@ -68,6 +68,7 @@ import org.whispersystems.textsecuregcm.push.PushNotificationManager;
 import org.whispersystems.textsecuregcm.registration.RegistrationServiceClient;
 import org.whispersystems.textsecuregcm.registration.RegistrationServiceException;
 import org.whispersystems.textsecuregcm.registration.RegistrationServiceSenderException;
+import org.whispersystems.textsecuregcm.registration.TransportNotAllowedException;
 import org.whispersystems.textsecuregcm.registration.VerificationSession;
 import org.whispersystems.textsecuregcm.spam.ScoreThresholdProvider;
 import org.whispersystems.textsecuregcm.storage.Account;
@@ -983,6 +984,38 @@ class VerificationControllerTest {
     }
   }
 
+  @Test
+  void requestVerificationCodeTransportNotAllowed() {
+    final String encodedSessionId = encodeSessionId(SESSION_ID);
+    final RegistrationServiceSession registrationServiceSession = new RegistrationServiceSession(SESSION_ID, NUMBER,
+        false, null, null,
+        null, SESSION_EXPIRATION_SECONDS);
+    when(registrationServiceClient.getSession(any(), any()))
+        .thenReturn(CompletableFuture.completedFuture(Optional.of(registrationServiceSession)));
+    when(verificationSessionManager.findForId(any()))
+        .thenReturn(CompletableFuture.completedFuture(
+            Optional.of(new VerificationSession(null, Collections.emptyList(), Collections.emptyList(), true,
+                clock.millis(), clock.millis(), registrationServiceSession.expiration()))));
+    when(registrationServiceClient.sendVerificationCode(any(), any(), any(), any(), any()))
+        .thenReturn(CompletableFuture.failedFuture(
+            new CompletionException(new TransportNotAllowedException(registrationServiceSession))));
+
+    final Invocation.Builder request = resources.getJerseyTest()
+        .target("/v1/verification/session/" + encodedSessionId + "/code")
+        .request()
+        .header(HttpHeaders.X_FORWARDED_FOR, "127.0.0.1");
+
+    try (final Response response = request.post(Entity.json(requestVerificationCodeJson("sms", "android")))) {
+      assertEquals(418, response.getStatus());
+
+      final VerificationSessionResponse verificationSessionResponse =
+          response.readEntity(VerificationSessionResponse.class);
+
+      assertTrue(verificationSessionResponse.allowedToRequestCode());
+      assertTrue(verificationSessionResponse.requestedInformation().isEmpty());
+    }
+  }
+
   @Test
   void requestVerificationCodeSuccess() {
     final String encodedSessionId = encodeSessionId(SESSION_ID);