Apple in its iPhone event said that users of the new iPhone 5 will be able to use FaceTime over cellular networks. This however was the line that Apple said, and doesn’t necessarily need to be supported by all the cellular networks.
Verizon has issued a statement which confirms the availability of FaceTime over its cellular network. AT&T on the other hand requires you to sign up an agreement or a deal that would allow you to use FaceTime over the cellular network, but you can still use FaceTime over WiFi.
FaceTime was never officially available over the cellular network, but there was a Cydia tweak that allowed users to use FaceTime over cellular networks, instead of just being restricted over WiFi. However, you do need to have some nice data plan, otherwise the data cap may burst.