Hopefully once Apple "opens" up facetime, they will also enable calls outside the Facetime network. Otherwise the who's and what's of connecting to their registrar will probably be no better than the App Store situation today (eg, I'm sure gateways will be forbidden).<p>edit: Although the identifying info from those screenshots is scrubbed, the comments say the R-URI is basically user@ip:port. This is interesting: there's no SIP proxy in between. No wonder it only works over wifi.
Its actually a little more complicated than that:<p><a href="http://www.packetstan.com/2010/07/special-look-face-time-part-3-call.html" rel="nofollow">http://www.packetstan.com/2010/07/special-look-face-time-par...</a>
Since Facetime is running SIP over WiFi, does AT&T still charge you minutes for a Facetime call or is that only for the non-facetime portion of the phonecall?
This is cool. This, Google Voice and Sipdroid on my Desire (which lets you route all calls, automatically, to the SIP provider of you choice, either on Wi-Fi only or 3G as well) makes me feel good about the future of telephony.