Are there any implementations of it that actually work well through NAT and which have a UI that non-technical people can use? We use Skype a lot - iChat would be fine, too, but seems to require port forwarding on both ends, which isn't going to happen anytime soon. Facetime forces you to use video, which isn't always what you want.
Google has just added WebRTC to the Chrome source tree. WebRTC (real-time communication) consists of Jingle, VP8, some voice codecs and other audio software they bought, and various NAT traversal algorithms. The IETF is standardising it and Mozilla and Opera are committed to shipping it. Somewhat interestingly, a bunch of Skype engineers seem to have been involved in it too.
The jingle portion of WebRTC comes form libjingle, and is usable right now with Google Talk. There is also a second open source implementation that works with Google Talk called "telepathy".
Gmail's voice and video chat works fine and has a pretty simple UI. I'm not sure it follows those specs completely but there are open-source clients that can connect to it. The Google client itself has pretty good Windows/OSX/Linux support as a browser plugin and with the Google Voice integration in Gmail you get a pretty full-featured UI to call both people that are on Google Talk and normal phones. Unfortunately the Google Voice stuff is still US only.
I did mention there were open-source implementations that could interface with it. I tested it against empathy (telepathy based) today and was pleasantly surprised with how well it worked. Previous attempts weren't as successful. I tried with both clients inside the same NAT though so I don't know if the firewall punching bits are as good.
Thanks for the clarification on the standards, it seems to have evolved since the early days.
