Earlier quoted context omitted.
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.
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 th…
And there are two open source implementations that it works with:
http://code.google.com/p/libjingle http://telepathy.freedesktop.org/wiki/