code: public int sms_sendMessageWithSession(Integer userId, CharSequence message)
      throws FacebookException, IOException {
      return extractInt(this.callMethod(FacebookMethod.SMS_SEND_MESSAGE,
                                 new Pair<String, CharSequence>("uid", userId.toString()),
                                 new Pair<String, CharSequence>("message", message),
                                 new Pair<String, CharSequence>("req_session", "1")));
    }
docs: Sends a message via SMS to the user identified by <code>userId</code>, with
  the expectation that the user will reply. The SMS extended permission is required for success.
  The returned mobile session ID can be stored and used in {@link #sms_sendResponse} when
  the user replies.
  
  @param userId a user ID
  @param message the message to be sent via SMS
  @return a mobile session ID (can be used in {@link #sms_sendResponse})
  @throws FacebookException in case of error, e.g. SMS is not enabled
  @throws IOException
  @see FacebookExtendedPerm#SMS
  @see <a href="http://wiki.developers.facebook.com/index.php/Mobile#Application_generated_messages">
  Developers Wiki: Mobile: Application Generated Messages</a>
  @see <a href="http://wiki.developers.facebook.com/index.php/Mobile#Workflow">
  Developers Wiki: Mobile: Workflow</a>