As one who has evaluated several VOIP over mobile applications, each was less than satisfactory given lack of quality of calls, similar to how first VOIP systems provided less than crystal clear calls.

VOIP over mobile applications are an issue as I learned, just check the TOS agreements with TMobile and AT&T and you will see they do not allow voice over their optional data networks. I doubt the carriers will allow anyone other than themselves to provide VOIP, and since it will reduce their profits, they will not be in a hurry to adopt VOIP while COIP is answer.

There’s one aspect that I think might be of an issue here – while there are silence periods in calls, can an operator design his capacity around that assumption or should he have enough bandwidth on a given cell to fit X calls without any silence?
I think this will break both the quality AND reliability assumptions set out by Garrett…

And it still means that VoIP takes more bandwidth than operators may be willing to sacrifice for “mere” voice calls at the moment.

Tsahi

Packet VoIP does not transmit silence, so over a longer conversation the average bandwidth will drop.

Not sure how the wireless carriers deal with full duplex today, but if they are honoring full duplex (and half the conversation is always silent), then the numbers may even favor VoIP