Buying it for a full price isn't the best idea, but it seems like T-mobile US likes to do a "buy one get one free" deal on those about 6 months after the release (that's how I did it last year with S8+). No contract either, the phone will just be locked to t-mobile until you pay the whole price, which you can do over 24 months (no extra charges) with the option to pay the whole thing off at any moment.