WebRTC http://www.webrtc.org/
While currently only available in-browser (Chrome and Firefox Nightly), it is actually a C++ Library and you can build native apps as well.
Ah, very nice hint, thanks for that! I see here:
https://code.google.com/p/libjingle/source/browse/trunk/talk...
That in fact your idea has a fair bit of merit. I will add "investigate adding libjingle to MOAI" to my MOAI to-do list, because .. it seems do'able.
Even a Lua implementation would be enough for me.