iPad Air LTE real life US carrier interchangebility

So, the iPad Air LTE is out. There is only one model number. The real question is, how's the real life interchangeability form carrier to carrier (something that no reviewers will ever mention).

I don't have the iPad Air, but from my experience of using the Verizon iPad 3, I know I can simply insert AT&T/T-Mobile SIM and get 3G service. So using that logic, it is safe to assume that if you pick Verizon as your initial carrier, you will be able to use it on the GSM carriers just fine.

But how about the other way around?

If one picks AT&T/T-Mobile as their starter carrier, can one simply put in a Verizon SIM and go? How about Sprint? We know that there is no excuse on the hardware side as all the radio bands are there.