Currenty, FaceTime only works over WiFi, so it has no impact on the plan from your carrier, and thus is "free", if your WiFi connection is free. When iOS 6.0 is introduced, FaceTime will be able to be done over 3G. This will use your carrier data plan. Note: carrier support for FaceTime, over 3G, is required in order to be able to FaceTime over 3G. In other words, even though you have "unlimited data", you carrier still must support FaceTime over 3G.