There are already a number of T-Mo iPhones on eBay. Be real careful. If the seller purchased the iPhone from T-Mo and purchased it using the $20/month deal then cancels their contract 1 or 2 or even 23 months from now without paying off the full price of the phone the phone will become a brick (for calls anyway). There really is no way to tell where the phone originated from or how it is being paid for even if you have the SN. There are a number of them on eBay for $600- $650 so I would certainly assume they were NOT bought from Apple for $679 or Tmobile for $580 but from T-Mo on the $99 down $20/month deal. You could be in for a big surprise anytime between now and TWO YEARS from now as T-Mo would kill the ESN and wouldn't reactivate it unless the full balance is paid off if the seller cancels their T-Mo contract which is easy to do now since there is no contract. Maybe it would work on ATT or another carrier but if you bought it for T-Mo you'd be in trouble.