One reason that many people chose to jailbreak their iPhone's was so they could do FaceTime over cellular (3G connection). Starting with iOS6, Apple will allow FaceTime when you are not on WiFi. Now, you can FaceTime where ever you are. Just watch your data plans, as FaceTime communicating uses around 90MB an hour, so if you are on a 2GB plan, you will get around 22 hours a month of FaceTime talking.
FaceTime over Cellular - iOS6