What region and network are you planing to use internet in?
T-Mobile operates in 3 LTE frequency bands in the US - B2, B4, B12 (for B12 the company planned to start operating just in July 2014) and 3 bands in the EU - B3, B7, B20, in depends of the region and license type. But Gobi 5000 (Sierra Wireless em7355) supports only 2 bands of 6 above - B2 and B4.
At the same time Sierra Wireless em7345 LTE card (another one card for the new line Lenovo notebooks) supports 5 bands of 6 above, except of B12.
So, there are no advantages for em7355 if you are not planning to work in Sprint LTE network and 3g CDMA/EV-DO networks of US carriers.
Supported frequency bands isn't a "locking" feature. It's a design, the set of components, filters. Purchase the card you need on shop.lenovo or altarnate resources.
x220 • Gobi 2000 3g | hdd, msata ssd, wwan, wifi, gps -- unique hand-made config ThinkPad 25 Special Anniversary Edition. #retro. Signed by D.Hill T470p | X1 Carbon Gen3 | Miix 2 10" | Yoga Tablet 2-1050F (Android) + BT Keyboard ThinkPad Stack • 2.4/5 Wireless Router, HDD 1 TB, BT Speaker, Power Bank, Mobile Projector