We are using JTAPI SendData API to send small alert messages to IP Phones. If specific phone is not connected in network the application gets timeout response. Can you please let us know , after how much time (after calling SendData method) application will get timeout response.
You should ideally check if terminal is in in-service state before calling sendData() method. This should eliminate most of your timeout errors.
'CTI Request Timeout' CTImanager service parameter determines the timeout value. The service parameter defaults to 5 seconds.