Rahul,
you did not tell me which model type you have so I can only tell you the basics. For any detailed configuration information, you will need to email me directly to discuss my services at mike_voip@hotmail.com
You first make sure passthru is set to No in the trunk group for FXO. You then set the forced IP Routing DN to a number that you want to send to the other side as the destination number. Again this is in the trunk group for the FXO. Finally, if you are not registering to a GK, then you must create a static route that points to the IP address of the device where you want all calls to go to and create a directory number pattern that matches the forced ip routing number, or you can just use ‘*’ for all calls.
You must submit and that should do it.