I can confirm this, as about two Thursdays ago, I noticed that FaceTime over Cellular turned ON by itself and I was able to test it successfully on my iPad 3 with the Unlimited Plan.
It was a pleasant, unexpected surprise. I just with they also enable Tethering, not that I use it a lot, but for those few times when I could really use it.
It was a pleasant, unexpected surprise. I just with they also enable Tethering, not that I use it a lot, but for those few times when I could really use it.