Yes T-Mobile's Simple Choice Tablet plans are compatible with iPad Air with LTE and Mini 3 with LTE.

The exception is if you must have 3G China Mobile coverage which uses TD-SCDMA, then you'd need to get the China only model.
http://en.wikipedia.org/wiki/TD-SCDMA
http://www.everymac.com/systems/appl...ina-specs.html

T-Mobile SIM works with GSM capable phones including the Verizon iPhone 4S. It will not work on older Verizon and Sprint phones without sim slots and 3G. They started to carry phones with sim slots for the LTE carrier info. GSMArena usually lists each phone's 3G bands, which you can reference with this chart http://www.worldtimezone.com/gsm.html If this makes your head ache, just get the current iPad or iPhone 5 or newer unlocked (either from Apple or carefully from large reputable sellers on eBay/Amazon).

You can also use iPad, LTE model or not, on wi-fi, of course. Skype, iMessage, e-mail, facebook and more will work via wi-fi connection. If you need internet access while away from wi-fi, get the LTE model and a tablet data plan.