Respect carrier setting indicating TTY is or isn't available.

Bug: 116764319
Test: Manual
Change-Id: Ie0ff020e0270deec1c81c29ae84d007df6d22691
diff --git a/src/com/android/phone/settings/AccessibilitySettingsFragment.java b/src/com/android/phone/settings/AccessibilitySettingsFragment.java
index 5c614d9..d540fba 100644
--- a/src/com/android/phone/settings/AccessibilitySettingsFragment.java
+++ b/src/com/android/phone/settings/AccessibilitySettingsFragment.java
@@ -93,7 +93,7 @@
         mButtonHac = (SwitchPreference) findPreference(BUTTON_HAC_KEY);
         mButtonRtt = (SwitchPreference) findPreference(BUTTON_RTT_KEY);
 
-        if (PhoneGlobals.getInstance().phoneMgr.isTtyModeSupported()) {
+        if (PhoneGlobals.getInstance().phoneMgr.isTtyModeSupported() && isTtySupportedByCarrier()) {
             mButtonTty.init();
         } else {
             getPreferenceScreen().removePreference(mButtonTty);
@@ -191,4 +191,15 @@
         }
         return false;
     }
+
+    /**
+     * Determines if the device supports TTY per carrier config.
+     * @return {@code true} if the carrier supports TTY, {@code false} otherwise.
+     */
+    private boolean isTtySupportedByCarrier() {
+        CarrierConfigManager configManager =
+                (CarrierConfigManager) mContext.getSystemService(Context.CARRIER_CONFIG_SERVICE);
+        return configManager.getConfig().getBoolean(
+                CarrierConfigManager.KEY_TTY_SUPPORTED_BOOL);
+    }
 }