The main requirements are:
- open source solution on Linux
- support P2P VoIP calls
- support presence
- support multicast VoIP announcements (and maybe some way of setting up such a "conference")
- preferably serverless (maybe the network can get split and I'd need to keep the functionality for all clients that still see each other)
I tried looking at telepathy, in particular telepathy-salut, but it seems to be quite a new technology, so it lacks clear/good documentation and/or working examples.
I'm also evaluating SIP (e.g. SofiaSIP), but it's working only if connected to a server.