That's not the case. There are a ton of unlocked phones on e-bay for example that will work with AT&T, T-Mobile, Cingular, etc, you just toss in a SIM from the carrier.

The issue is does the orig poster want a decent phone without any discount or one of the T-mobile ones with the discount.

I would recommend finding the phone you want elsewhere, and then getting the absolute lease expensive t-mobile phone and take the card out of it.