Add one new method is3gpp

Bug: 262735040
Test: atest android.telephony.cts.VisualVoicemailServiceTest
      Verified with live test that voice mail is received

Change-Id: Idae7ad9580f3c98e5f253e9e0627f68f5f87967b

telephony/java/android/telephony/SmsMessage.java

@@ -1030,6 +1030,15 @@ public class SmsMessage {
         return mWrappedSmsMessage.getReceivedEncodingType();
     }
 
+    /**
+     * Check if format of the message is 3GPP.
+     *
+     * @hide
+     */
+    public boolean is3gpp() {
+        return (mWrappedSmsMessage instanceof com.android.internal.telephony.gsm.SmsMessage);
+    }
+
     /**
      * Determines whether or not to use CDMA format for MO SMS.
      * If SMS over IMS is supported, then format is based on IMS SMS format,