If you;re already a T-mobile user you can get a free upgrade phone for signing a contract extension for a year. I had one of those really old Nokias with the black and green LCD, I was able to get a phone half the size with twice the battery for simply agreeing to continue using T-mobile for another year.(which I was going to do anyway since I have the cheapest possible plan they offer)
Of course you'd still have to pay like 50 bucks if you want to move up from a black and white phone to one with a color screen and or internet features.