I installed TextSecure Server.(https://github.com/WhisperSystems/TextSecure-Server)
I also modified some server side code to to simplify registration process and to accept predefined sms/voice verification code.
I also created custom TextSecure app with my own TextSecure server details. And installed on my two android devices. I successfully registered TextSecure app on my two mobiles. No problem at all.
But when I send message from one mobile, server gets this message, but not able to connect to GCM push framework, and send this message to another mobile as a SMS. The message contents are in encrypted form. I don't understand what are gcm push frameworks credentials (host, port, username, password) that I need to mention in yml configuration file.