how the iphone/ipod touch connects to others when making a video call over wifi

I've searched everywhere for this but haven't found anything.

I'm trying to understand what APIs/classes are used when ma开发者_如何学Goking a video chat. More specifically how does the iphone/ipod touch use your contact list to connect to another one over wifi and then how does it do voice and video. Is the contact list on an apple server that it uses to connect through to?

Thanks A.R.

I Googled and this came up