From Apple -
FaceTime video calling requires a FaceTime-enabled device for the caller and recipient and a Wi-Fi connection. FaceTime over a cellular network requires iPhone 4s, iPhone 5, or iPad (3rd generation) with cellular data capability. Availability over a cellular network depends on carrier policies; data charges may apply.
Cheers, Tom
http://bgr.com/2012/03/15/facetime-not-supported-over-lte-on-the-new-ipad/
Message was edited by: Texas Mac Man