Sprint won't charge for FaceTime over 3G or 4G on the iPhone 5, iPhone 4S or iPhone 4
One of the cool new features of the iPhone 5 and iDevices running iOS 6 will be the ability to use FaceTime over cellular networks, and Sprint has confirmed that you'll be able to make video calls on its network without having to pay extra.
Verizon also said that it won't charge extra to make FaceTime calls over its network as these video calls will just eat into your pool of data. Sprint is the only major carrier offering the iPhone 5 with an unlimited data plan, so I suppose you could use your Sprint iPhone 5 and only make FaceTime calls and not have to worry about it.
It looks like AT&T is the only carrier that is charging more for FaceTime, as users have to switch to the Mobile Share plan to use it. Remember, you can always use FaceTime video calling for free on Wi-Fi networks.