diff --git a/src/com/android/phone/PhoneInterfaceManager.java b/src/com/android/phone/PhoneInterfaceManager.java
index 073606f..e1a9592 100755
--- a/src/com/android/phone/PhoneInterfaceManager.java
+++ b/src/com/android/phone/PhoneInterfaceManager.java
@@ -5320,14 +5320,19 @@
     }
 
     /**
-     * Determines whether the user has turned on RTT. Only returns true if the device and carrier
-     * both also support RTT.
+     * Determines whether the user has turned on RTT. If the carrier wants to ignore the user-set
+     * RTT setting, will return true if the device and carrier both support RTT.
+     * Otherwise. only returns true if the device and carrier both also support RTT.
      */
     public boolean isRttEnabled(int subscriptionId) {
         final long identity = Binder.clearCallingIdentity();
         try {
-            return isRttSupported(subscriptionId) && Settings.Secure.getInt(
+            boolean isRttSupported = isRttSupported(subscriptionId);
+            boolean isUserRttSettingOn = Settings.Secure.getInt(
                     mApp.getContentResolver(), Settings.Secure.RTT_CALLING_MODE, 0) != 0;
+            boolean shouldIgnoreUserRttSetting = mApp.getCarrierConfigForSubId(subscriptionId)
+                    .getBoolean(CarrierConfigManager.KEY_IGNORE_RTT_MODE_SETTING_BOOL);
+            return isRttSupported && (isUserRttSettingOn || shouldIgnoreUserRttSetting);
         } finally {
             Binder.restoreCallingIdentity(identity);
         }
diff --git a/src/com/android/phone/settings/AccessibilitySettingsFragment.java b/src/com/android/phone/settings/AccessibilitySettingsFragment.java
index cff9c0a..b074f20 100644
--- a/src/com/android/phone/settings/AccessibilitySettingsFragment.java
+++ b/src/com/android/phone/settings/AccessibilitySettingsFragment.java
@@ -160,10 +160,16 @@
             int rttMode = mButtonRtt.isChecked() ? 1 : 0;
             Settings.Secure.putInt(mContext.getContentResolver(), Settings.Secure.RTT_CALLING_MODE,
                     rttMode);
-            // Update RTT config with IMS Manager
-            ImsManager imsManager = ImsManager.getInstance(getContext(),
-                    SubscriptionManager.getDefaultVoicePhoneId());
-            imsManager.setRttEnabled(mButtonRtt.isChecked());
+            // Update RTT config with IMS Manager if the always-on carrier config isn't set to true.
+            CarrierConfigManager configManager = (CarrierConfigManager) mContext.getSystemService(
+                            Context.CARRIER_CONFIG_SERVICE);
+            for (int subId : SubscriptionController.getInstance().getActiveSubIdList(true)) {
+                if (!configManager.getConfigForSubId(subId).getBoolean(
+                        CarrierConfigManager.KEY_IGNORE_RTT_MODE_SETTING_BOOL, false)) {
+                    ImsManager imsManager = ImsManager.getInstance(getContext(), subId);
+                    imsManager.setRttEnabled(mButtonRtt.isChecked());
+                }
+            }
             return true;
         }
 
@@ -193,18 +199,23 @@
     }
 
     private boolean shouldShowRttSetting() {
-        int subscriptionId = SubscriptionManager.getDefaultVoiceSubscriptionId();
-        if (subscriptionId == SubscriptionManager.INVALID_SUBSCRIPTION_ID
-                || subscriptionId == SubscriptionManager.DEFAULT_SUBSCRIPTION_ID) {
-            for (int subId : SubscriptionController.getInstance().getActiveSubIdList(true)) {
-                if (PhoneGlobals.getInstance().phoneMgr.isRttSupported(subId)) {
+        CarrierConfigManager configManager =
+                (CarrierConfigManager) mContext.getSystemService(Context.CARRIER_CONFIG_SERVICE);
+        // Go through all the subs -- if we want to display the RTT setting for any of them, do
+        // display it.
+        for (int subId : SubscriptionController.getInstance().getActiveSubIdList(true)) {
+            // In order to display the setting, we want:
+            // 1. The subscription supports RTT
+            // 2. The subscription isn't configured by the carrier to have the setting always-on
+            //    (see the documentation for the carrier config key)
+            if (PhoneGlobals.getInstance().phoneMgr.isRttSupported(subId)) {
+                if (!configManager.getConfigForSubId(subId).getBoolean(
+                        CarrierConfigManager.KEY_IGNORE_RTT_MODE_SETTING_BOOL, false)) {
                     return true;
                 }
             }
-            return false;
-        } else {
-            return PhoneGlobals.getInstance().phoneMgr.isRttSupported(subscriptionId);
         }
+        return false;
     }
 
     /**