Despite Apple's new iPad sporting 4G LTE connectivity, oddly enough it appears that attempting to make FaceTime video calls over a faster LTE connection is still not allowed. It seems that when attempting to make a FaceTime call over a LTE connection, an error message pops up stating that FaceTime has failed, prompting the user to connect to a WiFi network to continue.
Ubergizmo, The new iPad's FaceTime will not work over 4G LTE