No, it is not possible. First of all, the enV is a
CDMA phone, T-Mobile is a
GSM network. Second,
CDMA phones do not "unlock" the way that
GSM phones do. Because of the inherent security built into
CDMA networks, you can not take a phone from one network to use on another (ie: using a Verizon phone on Sprint's network). Sell the phone on eBay. If it's in decent shape and not on Verizon's stolen
ESN list, you might get a couple hundred bucks for it!