Earlier this year they did away with the "lock you in" style contracts that the mainstream telcom providers use to keep people on their expensive plans. It is SIM-card based so I bought a pretty good phone on ebay for cheap and it works... but the main reason T-Mobile is awesome is that if you have an unlimited data +texts plan in the states then you have:
Unlimited International Data and Texts
Imagine this, you cross the border and get a text from T-Mobile with these sweet sweet words
"Welcome to South Korea, Unlimited web included as part of your global coverage" ... "Unlimited text incl with your global coverage."I had a layover of only a couple of hours Incheon but in that time I found out what the currency was worth, read the Wikipedia page about the city and observed my exact position and local area with GPS.
With unlimited data you can hop on a random bus in a random city and know that you can Google for directions back, find hotels nearby or book a flight. The experience of international travel has fundamentally changed to one of previously unimaginable convenience.
Thank you T-Mobile!