If VOIP over 3G is enabled, it is the beginning of the end for the profits of the big cell phone providers. They will be relegated to being a "utility" or commodity provider.
More likely they'll set data prices such that a VoIP call costs more than a circuit-switched voice call. This wouldn't even be evil, since a VoIP call uses more bandwidth than a circuit-switched call.
They could also do what 3 have done in the UK with Skype - all their new phones have a 3-produced Skype app preloaded which appears to work just like any other installation of Skype.
Behind the scenes, updating your contact list and sending / receiving IMs are done over the data network - however, when you make or receive a Skype call it's routed over the voice network and simply not charged.
The IMs are 1kBit of data, whereas a phone call (considering voice coding at 16kBit/s for skype-ish quality) probably amount to megabytes of data having to go at near-realtime rates.
It's good that they're still in business, I suppose.
those big cell phone providers being the same ones providing the data network to carry the voip calls, of course.
it wouldn't be a stretch for at&t to claim their feeble network can't support voip and block it or just deprioritize voip packets enough that the calls are not clear.
