I've posted this in the other
one lte model thread but here are my findings from personal experience with verizon ipad air.
Verizon ipad air absolutely works on all of AT&T networks (lte and 3G). It will activate over the air an unactivated verizon sim. It will not activate over the air an unactivated AT&T sim. However, if you connect to wifi you can activate an unactivated AT&T sim. Once the AT&T sim is activated you can manage it over the air, cancel and restart plans and even after the data plan is canceled(account not canceled just the plan).
I had no problem cutting down my micro sim from my verizon ipad3 and having it work in my verizon ipad air. However, I had problems accessing my account on the iPad. I couldn't sign in to view, add or cancel my plan. It would keep asking me to reprovision my device. Called verizon tech support and ran through all the steps with no results. Told me it was a problem with iPads firmware. Went to apple had it checked out, did a dfu restore myself, nothing. I did a search and seems to be a common problem with verizon...and only solution really seemed like getting a new sim and having the account switched over to a new sim.....which worked for me.