@Override
 public void onPlayDtmfTone(char c) {
   final TelephonyConnection connection = getFirstConnection();
   if (connection != null) {
     connection.onPlayDtmfTone(c);
   }
 }
 @Override
 public void onStopDtmfTone() {
   final TelephonyConnection connection = getFirstConnection();
   if (connection != null) {
     connection.onStopDtmfTone();
   }
 }
 /** Invoked when the conference should be moved from hold to active. */
 @Override
 public void onUnhold() {
   final TelephonyConnection connection = getFirstConnection();
   if (connection != null) {
     connection.performUnhold();
   }
 }