Here's a somewhat related question on peer to peer systems.

Is there peer to peer VoIP that works? Discovering the other end isn't a problem; this is chat for a game, so there's a way to tell the other end about IP addresses and such. The question is whether you can reliably set up a VoIP connection between N known endpoints, including proper echo suppression and conference bridging, without a central server. Are the issues of getting through firewalls with cooperation from both sides solved? Is there anything that works well enough that non-technical users can use it reliably?