It is known that Apple and AT&T have an agreement to block VoIP applications from using AT&T’s mobile network. However an article on zdnet states VoIP apps using WiFi are fine.
The Apple and AT&T agreement is stated in a letter sent to the FCC by AT&T. The letter clarifies that AT&T and Apple agree that Apple will not enable the iPhone to uses AT&T’s wireless service (2G, 3G and WiFi) to make VoIP calls without accessing consent from AT&T.
It is suggested that without this agreement the price of the iPhone would have been greater than it is. AT&T frequently review their capability and feature policies, and are said to take a “fresh look” at the possibility of authorising VoIP capabilities on the AT&T 3G network for the iPhone. For more information head to phonesreview.
