its a lease to own program. You're still paying off your principle balance with every payment and there is no interest in said balance. If you want to buy the phone out you just pay whatever the leftover msrp minus the monthly payments you have made towards said device is. But you bring up a good point. Every other program requires sales tax up front which is why I asked. I wasn't sure if tmo is just eating the sales tax or what.
I just checked the small print. Tax is additional. But I question your comment about "lease to own". You start out turning over your existing phone to them. If you trade in during the 18 months on a new phone you get a new lease. At the end of the lease you either turn the phone back in or "pay it off" so it's like any other lease. But the strong temptation at that point would be to turn it in on a new phone. If paying it off is the difference between msrp and the lease payments (the website doesn't say!) then that would be another $164 or 6 months of payments on a new lease. It's easy to guess what most people will do -- renew the phones on lease forever. Most people will never own the phone.