LB2120 – 4G LTE Modem - fully supported on T-Mobile network??

I don't know.. its should. It does with a GoogleFi phone or data SIM which uses the Sprint data network. T-Mobile and Sprint seem to be converging in some ways. The key is obtaining and getting the "actual" APN for your carrier.. more specifically the [one APN] they want you to use. An APN is like a WiFi network name, which your device will use to connect to T-Mobile, if you get it wrong or try to connect to the [wrong] APN, or the default APN for T-Mobile, it will throttle you to 3G and repeatedly throw you off and block traffic. You will not get an error message from the network, and the LB2120 will have no error information to show you.. it just will not work. The carriers often don't train their people to "know" what the APN is, and sometimes they issue a different APN for different locations within the same regional market.. so it can be a bit like a mystery. The LB2120 will "automatically" try the "default" APN broadcast by the carrier.. which is usually "blocked" and used to catch stray connections and throw them off their network as a security measure.. its like "flypaper". The LB2120 has a manual override to enter in the correct APN for your carrier and save it as the one to use on reboot. Then it will not try to use the carrier "default" APN, it will use the correct one and your LB2120 will lock on and be granted 4G access. Generally that is the test to pass.. if your 3G it means your stuck on "flypaper", if your granted 4G you've been granted access to the Internet.