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 58a79d49c..72ff01d61 100644
--- a/service/src/main/java/org/whispersystems/textsecuregcm/controllers/VerificationController.java
+++ b/service/src/main/java/org/whispersystems/textsecuregcm/controllers/VerificationController.java
@@ -193,6 +193,8 @@ public class VerificationController {
 
       registrationServiceSession = registrationServiceClient.createRegistrationSession(phoneNumber, sourceHost,
           accountsManager.getByE164(request.number()).isPresent(),
+          request.updateVerificationSessionRequest().mcc(),
+          request.updateVerificationSessionRequest().mnc(),
           REGISTRATION_RPC_TIMEOUT).join();
     } catch (final CancellationException e) {
 
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 73a166d95..b3db545b5 100644
--- a/service/src/main/java/org/whispersystems/textsecuregcm/registration/RegistrationServiceClient.java
+++ b/service/src/main/java/org/whispersystems/textsecuregcm/registration/RegistrationServiceClient.java
@@ -94,7 +94,12 @@ public class RegistrationServiceClient implements Managed {
   }
 
   public CompletableFuture<RegistrationServiceSession> createRegistrationSession(
-      final Phonenumber.PhoneNumber phoneNumber, final String sourceHost, final boolean accountExistsWithPhoneNumber, final Duration timeout) {
+      final Phonenumber.PhoneNumber phoneNumber,
+      final String sourceHost,
+      final boolean accountExistsWithPhoneNumber,
+      @javax.annotation.Nullable final String clientMcc,
+      @javax.annotation.Nullable final String clientMnc,
+      final Duration timeout) {
 
     final long e164 = Long.parseLong(
         PhoneNumberUtil.getInstance().format(phoneNumber, PhoneNumberUtil.PhoneNumberFormat.E164).substring(1));
@@ -105,6 +110,8 @@ public class RegistrationServiceClient implements Managed {
             .setE164(e164)
             .setAccountExistsWithE164(accountExistsWithPhoneNumber)
             .setRateLimitCollationKey(rateLimitCollationKey)
+            .setMcc(clientMcc != null ? clientMcc : "")
+            .setMnc(clientMnc != null ? clientMnc : "")
             .build()), callbackExecutor)
         .thenApply(response -> switch (response.getResponseCase()) {
           case SESSION_METADATA -> buildSessionResponseFromMetadata(response.getSessionMetadata());
diff --git a/service/src/main/proto/RegistrationService.proto b/service/src/main/proto/RegistrationService.proto
index d54c744ec..a3ad8935a 100644
--- a/service/src/main/proto/RegistrationService.proto
+++ b/service/src/main/proto/RegistrationService.proto
@@ -45,6 +45,16 @@ message CreateRegistrationSessionRequest {
    * collated by this key.
    */
   string rate_limit_collation_key = 3;
+
+  /**
+   * The MCC for the given `e164` as reported by the client.
+   */
+  string mcc = 4;
+
+  /**
+   * The MNC for the given `e164` as reported by the client.
+   */
+  string mnc = 5;
 }
 
 message CreateRegistrationSessionResponse {
diff --git a/service/src/test/java/org/whispersystems/textsecuregcm/configuration/StubRegistrationServiceClientFactory.java b/service/src/test/java/org/whispersystems/textsecuregcm/configuration/StubRegistrationServiceClientFactory.java
index 80692a2e6..d566a599e 100644
--- a/service/src/test/java/org/whispersystems/textsecuregcm/configuration/StubRegistrationServiceClientFactory.java
+++ b/service/src/test/java/org/whispersystems/textsecuregcm/configuration/StubRegistrationServiceClientFactory.java
@@ -61,7 +61,12 @@ public class StubRegistrationServiceClientFactory implements RegistrationService
 
     @Override
     public CompletableFuture<RegistrationServiceSession> createRegistrationSession(
-        final Phonenumber.PhoneNumber phoneNumber, final String sourceHost, final boolean accountExistsWithPhoneNumber, final Duration timeout) {
+        final Phonenumber.PhoneNumber phoneNumber,
+        final String sourceHost,
+        final boolean accountExistsWithPhoneNumber,
+        @javax.annotation.Nullable final String clientMcc,
+        @javax.annotation.Nullable final String clientMnc,
+        final Duration timeout) {
 
       final String e164 = PhoneNumberUtil.getInstance()
           .format(phoneNumber, PhoneNumberUtil.PhoneNumberFormat.E164);
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 b8856d245..47f6b1393 100644
--- a/service/src/test/java/org/whispersystems/textsecuregcm/controllers/VerificationControllerTest.java
+++ b/service/src/test/java/org/whispersystems/textsecuregcm/controllers/VerificationControllerTest.java
@@ -192,7 +192,7 @@ class VerificationControllerTest {
 
   @Test
   void createSessionRateLimited() {
-    when(registrationServiceClient.createRegistrationSession(any(), anyString(), anyBoolean(), any()))
+    when(registrationServiceClient.createRegistrationSession(any(), anyString(), anyBoolean(), any(), any(), any()))
         .thenReturn(CompletableFuture.failedFuture(new RateLimitExceededException(null)));
 
     final Invocation.Builder request = resources.getJerseyTest()
@@ -206,7 +206,7 @@ class VerificationControllerTest {
 
   @Test
   void createSessionRegistrationServiceError() {
-    when(registrationServiceClient.createRegistrationSession(any(), anyString(), anyBoolean(), any()))
+    when(registrationServiceClient.createRegistrationSession(any(), anyString(), anyBoolean(), any(), any(), any()))
         .thenReturn(CompletableFuture.failedFuture(new RuntimeException("expected service error")));
 
     final Invocation.Builder request = resources.getJerseyTest()
@@ -221,7 +221,7 @@ class VerificationControllerTest {
   @ParameterizedTest
   @MethodSource
   void createBeninSessionSuccess(final String requestedNumber, final String expectedNumber) {
-    when(registrationServiceClient.createRegistrationSession(any(), anyString(), anyBoolean(), any()))
+    when(registrationServiceClient.createRegistrationSession(any(), anyString(), anyBoolean(), any(), any(), any()))
         .thenReturn(
             CompletableFuture.completedFuture(
                 new RegistrationServiceSession(SESSION_ID, requestedNumber, false, null, null, null,
@@ -238,7 +238,7 @@ class VerificationControllerTest {
 
       final ArgumentCaptor<Phonenumber.PhoneNumber> phoneNumberArgumentCaptor = ArgumentCaptor.forClass(
           Phonenumber.PhoneNumber.class);
-      verify(registrationServiceClient).createRegistrationSession(phoneNumberArgumentCaptor.capture(), anyString(), anyBoolean(), any());
+      verify(registrationServiceClient).createRegistrationSession(phoneNumberArgumentCaptor.capture(), anyString(), anyBoolean(), any(), any(), any());
       final Phonenumber.PhoneNumber phoneNumber = phoneNumberArgumentCaptor.getValue();
 
       assertEquals(expectedNumber, PhoneNumberUtil.getInstance().format(phoneNumber, PhoneNumberUtil.PhoneNumberFormat.E164));
@@ -262,7 +262,7 @@ class VerificationControllerTest {
         .format(PhoneNumberUtil.getInstance().getExampleNumber("BJ"), PhoneNumberUtil.PhoneNumberFormat.E164);
     final String oldFormatBeninE164 = newFormatBeninE164.replaceFirst("01", "");
 
-    when(registrationServiceClient.createRegistrationSession(any(), anyString(), anyBoolean(), any()))
+    when(registrationServiceClient.createRegistrationSession(any(), anyString(), anyBoolean(), any(), any(), any()))
         .thenReturn(
             CompletableFuture.completedFuture(
                 new RegistrationServiceSession(SESSION_ID, NUMBER, false, null, null, null,
@@ -283,7 +283,7 @@ class VerificationControllerTest {
   @MethodSource
   void createSessionSuccess(final String pushToken, final String pushTokenType,
       final List<VerificationSession.Information> expectedRequestedInformation) {
-    when(registrationServiceClient.createRegistrationSession(any(), anyString(), anyBoolean(), any()))
+    when(registrationServiceClient.createRegistrationSession(any(), anyString(), anyBoolean(), any(), any(), any()))
         .thenReturn(
             CompletableFuture.completedFuture(
                 new RegistrationServiceSession(SESSION_ID, NUMBER, false, null, null, null,
@@ -317,7 +317,7 @@ class VerificationControllerTest {
   @ParameterizedTest
   @ValueSource(booleans = {true, false})
   void createSessionReregistration(final boolean isReregistration) throws NumberParseException {
-    when(registrationServiceClient.createRegistrationSession(any(), anyString(), anyBoolean(), any()))
+    when(registrationServiceClient.createRegistrationSession(any(), anyString(), anyBoolean(), any(), any(), any()))
         .thenReturn(
             CompletableFuture.completedFuture(
                 new RegistrationServiceSession(SESSION_ID, NUMBER, false, null, null, null,
@@ -341,6 +341,8 @@ class VerificationControllerTest {
           eq(PhoneNumberUtil.getInstance().parse(NUMBER, null)),
           anyString(),
           eq(isReregistration),
+          any(),
+          any(),
           any()
       );
     }