My wife and I both have same iPhone 4 (not 4s) model number A1332 and same network and contracts. Hers can use FaceTime over 3G but mine can't. What could be stopping mine from doing this? Before you say one of ours is a 4s, they aren't, and she definitely gets FaceTime over 3G as can do it with our router switched off and wifi switched off but I can't
From here http://www.apple.com/ios/facetime/, the following information is provided.
Call it what you want.