Funny I had the same question right before Christmas. Come to find out I know nobody with T-Mobile, and a couple people who had them a few years back, was unhappy with them.
I end up going with VM, but with the wildfire because of the 100 off. I never really use the internet with the phone, until I quickly grew unhappy with the memory of the phone. I rooted the phone to get rid off bloatware, and figured if i was going to root being my first, I add wireless teathering and some other recommend apps. I never really used the tethering unitll, the past few weeks. Just to find out last week I started to play order and chaos at work for 4hr'5days a week and 2hr a day on the weekends with my daughters nook for Netflix. I'm pritty sure I'm well over my 2.5g with no cap as of yet. If i did not have time to play the game, I streamed Netflix with no one watching, just to test this out.