http://en.wikipedia.org/wiki/List_of_LTE_networks
Qualcomm offers a baseband which can support many bands but most devices support just the bands in the region which the SKU is targeted for. Most manufacturers split off the US/NA from the rest of the world.
iPad Air and Mini Retina have the most number of LTE bands supported.
* Wi-Fi (802.11a/b/g/n); dual channel
(2.4GHz and 5GHz) and MIMO
* Bluetooth 4.0 technology
* UMTS/HSPA/HSPA+/DC-HSDPA (850, 900, 1900, 2100 MHz); GSM/EDGE (850, 900, 1800, 1900 MHz)
* CDMA EV-DO Rev. A and Rev. B (800, 1900 MHz)
* LTE (Bands 1, 2, 3, 4, 5, 7, 8, 13, 17, 18, 19, 20, 25, 26)3
* Data only4