its the iphone 4 not 4g. 4g for att still doesnt come out. 4g is a diffrent level of internet wich is faster. so the iphone4 can only facetime with iphone 4's itouch4 mac's and macbooks well only apple tech. but imma give you a little advice. the iphone5 wellbe coming out in june so if you get the iphone4 now youll be stuck with it. so i advice you to wait tell june or july thern with that iphone u would probably be able to do that!
Thank you!