This thread is pretty funny. The Facetime on the iPhone is a feature built in but its an App you open just like everything you do on your phone, this feature will definitely use data its not free so even tho you are being allowed to use Facetime on your phone guess what you are going to eat up your 3GB of data you have with ATT like nothing. Video calls use huge amounts of data just like video streaming. So sure youll get access but guess what on ATT's network youll rack up those overages quick so good luck with that ;). The reason it was only available on WiFi before was mainly because of quality of video during a call and also because of the amount of bandwidth and strain it would put on ATT's network.
Skype is the same thing with a few additional features and it will definitely use data, its an app, and even tho it will be a built in feature on the Windows 8 phones coming out soon its not going to be a free feature so keep dreaming