As we now know, iOS 6 finally enables the feature legitimately without needing to jailbreak to use the video-calling feature over a cellular network, be it Edge, 3G, or even 4G. The only actual barrier from being able to do it now, are the carriers themselves. A statement from AT&T today reveals that AT&T will only allow those on shared family plans to use FaceTime over cellular on their iPhones:
Originally Posted by AT&T
The bad news on the other hand, is that individuals with their own non-family plan cellular plans with AT&T will not be able to use the feature whatsoever under AT&T’s dictating terms, however that's not to say that jailbreak tweaks won’t fix this. Although AT&T will be limiting FaceTime over cellular to their family plan subscribers, users still have the ability to use the feature from their home Wi-Fi networks and over public Wi-Fi networks wherever available as carrier have no control over what is done from the user's own internet access. Users can also tether to other phones as hotspots and use the feature.
Sprint and Verizon both will not limit their iPhone’s ability to support FaceTime over cellular networks as AT&T plans to do. For most people, since FaceTime is not a necessary function of having a phone, the announcement won’t impede people’s abilities to use their iPhones. That being said, FaceTime over cellular probably isn’t something important enough that people are going to leave AT&T and hop over to another company for.