i'm new to SIP. I want to integrate my existing Instant Messenger to SIP server. I mean i have to write some thing so that our IM users can chat with the other users using SIP. But i don't know SIP. Now i'm going through SIP docs. I'm getting the architecture, but i'm unable to understand what to write for the above problem. Whether we need to write one SIP enabled server or we have to use third party server. So please let me know what actually i need to do to get out from this problem.