In light of the Vonage app which was approved the other day, I don't see what possible objection ATT/Apple could have against the Google Voice application.
Remember: it's not an objection to VOIP in general. It's an objection to the replacement of core iPhone functionality.
EDIT: Hey everybody. I'm just repeating what Apple said. The GV announcement said nothing about VOIP, it just said "replacement of core functionality." Thanks.
Perhaps I'm just old-fashioned, but I would have thought that the piece of software in the iPhone that makes it usable as a phone would be closer to "core functionality" than the dialer. VOIP is definitely treading on the former, though how it deals with the latter is obviously a question of interface rather than of protocol.
I appreciate Apple's attempts maintain integrity in the UI interface but their hysterics over something like this make me wary.
AT&T has always limited iPhone VoIP applications to WiFi to cripple their usefulness. They just announced today that they were extending VoIP apps to 3G, most likely due to pressure from the FCC.
Also, you can't replace the native dialer or any core functions on the iPhone. Google Voice implemented its own dialing interface and was rejected for duplicating the built-in dialing and voicemail functions.
http://finance.yahoo.com/news/ATT-Extends-VoIP-to-3G-bw-7675...
http://en.wikipedia.org/wiki/Google_voice#Rejection_from_iPh...