I had Verizon and moved to T-Mobile.. I have been VERY happy during the first month. Verizon can't seem to bill me correctly so I thought I would try someone new. T-Mobile's service has been outstanding. I have not had one dropped call (can't say that about Verizon). And I really like the fact that I can easily change phones based on my mood for that day.

I will admit I have not been everywhere just yet but the major areas in DC seem to be covered (Capital Hill.. Dupont.. etc..) Except the Metro in the underground sections which is only covered by Verizon (and Sprint but you will be roaming) The entire 66/267 Dulles route works without a hitch.

Good luck.. And don't drop T-Mobile because of the perception that Verizon is better.. My experience is that service has deteriorated and they can't seem to fix billing errors.