Apple iPad Air and iPad mini 2 with Retina support more LTE bands than any mobile device

That's the most out of any mobile device, and, depending on which version of the iPad Air or iPad mini 2 with cellular connectivity you get, you will be able to hook them up to most LTE carrier networks worldwide with a single device, which has been a dream come true for a while now. The biggest winner is T-Mobile, whose 4G offering is now supported, which can't be said for Sprint's Time-Division LTE peculiarity, Japan's SoftBank, China Mobile and a few other carriers in Asia and the Middle East for now, so 4G connection on those may be spotty, depending on what tower equipment you are in the vicinity of.

Of course, Apple is cautioning that it depends on individual carrier settings, saying that "iPad models are unlocked and may support LTE networks outside the country of purchase when using a valid SIM from a supported carrier. Contact your carrier for more details," but if the experience with the new iPhones is any indication, most of the times you can just pop a local LTE SIM card if you've bought your device without a contract, and enjoy the blazing download speeds that the local carrier in question offers you.

source: Apple