SOrry to be a broken record, but Sococo's product does all of this. IT uses P2P when it works; else it routes through a 'media node' when necessary, all automatically and on the fly. You can be walking around with your wireless laptop on VPN talking and video-chatting; stop at your desk and plug in, and all the streams switch almost-seamlessly.

Caveat: I work at Sococo (I architected the audio/networking system).