I am waiting to pre-order an iPad pro, and I am contemplating whether or not to get a cellular model. One argument in favor of the cellular model is the Apple SIM card. It would be convenient to be able to change carriers without swapping SIM cards. When the Apple SIM card first came out, I seem to remember that T-Mobile would not "lock" the SIM, while AT&T would lock it if you activated it on their network. Is this still true? If so, it really defeats the purpose of having a non-carrier SIM card.