Already announced a while back. All EDGE to LTE by the end of summer 300M POPs covered in LTE by year end 2015.
http://www.tmonews.com/2015/02/t-mobiles-lte-coverage-map-will-look-like-this-by-the-end-of-2015/
When this happens I will give them another shot. Used their trial program and roamed a bunch on ATT lol.