As of the release of iOS 6 in 2012, FaceTime works over a 3G or 4G network connection on iPhones running iOS 6 or later. FaceTime also works on the iPhone 4S or later and third generation or later iPads.
Certain providers may set limits on the usage of FaceTime over the provider's network, though the exact limitations vary. Prior to iOS 6, FaceTime was only usable over a Wi-Fi connection. To activate FaceTime for use over cellular networks on Apple products running iOS 6 and later, open the Settings application and allow FaceTime to use cellular data in its operation.