Today, at a media event in New York, T-Mobile announced that it's finally ready to join the big-boy world of LTE networks. The initial round of activations match up just about perfectly with the earlier leaks. Major cities include Houston, Las Vegas, Washington D.C. and more. The proper 4G network can be used with the new "Uncarrier" plans that just went live a couple days ago.
Here's the full list of launch cities: