I forgot to mention that a T-mobile store can't really do anything with the phone. Only tech support is authorized to place an order for a warranty replacement. I work for t-mobile and unfortunately the majority of reps you will find in the stores don't know the first thing about troubleshooting a windows phone. If flashing a shipped rom doesn't solve the problem, your best bet is to contact tech support directly and they will have you hard reset the phone then order a replacement.