For some time now it has been looming, the question of VoIP on the iPhone that is. Well apparently no more! Steve Jobs said at an SDK launch: “ VoIP will be available on the iPhone if it is not using to use EDGE network.”
Furthermore, iPhone SDK doc states: “If an Application requires or will have access to the carrier network, then additionally such Application: …May not have Voice over Internet Protocol (VoIP) functionality.”
What this means is VoIP applications need to be specifically written for the WiFi network; hopefully it won’t take some developer to come up with a rewritten application, and once that happens VoIP will be on the iPhone!
Source — arstechnica