It is possible that they are getting the 9520, but beyond Rogers we have not heard of any other carriers getting that device. Some evidence suggests Verizon would cry foul if Tmo got the 9520, but we shall see.
If you want a Storm on Tmo right now, you can get a 9530 unlocked and use it on Tmo. It would be limited to EDGE thou, and it does not have wifi or UMA.
You are probably better off with a 8900 Curve, or 8220 Flip, OR waiting on the possibilty of the 9520.