I'm not sure if you'll read this, since it's been so long, but here goes. Depending on what you plan to do, if you want to be 'standards compliant', I'd look i

I'm not sure if you'll read this, since it's been so long, but here goes. Depending on what you plan to do, if you want to be 'standards compliant', I'd look into SIP, and it's IM extension called SIMPLE. What's interesting here is, that the 3GPP body - defining the telco standards of the future - has chosen SIP as it's signalling protocol for media sessions (voice + video), but also for IM. In addition there is a 'network address book' (= server side contact list) standard based on XCAP. All of the above are part of what's called IMS, the IP based communications infrastructure for future telco networks. A good library for SIP client development is PJSIP. If you are just in need of a good IM infrastructure, XMPP/Jabber seems to be better suited.