Just keep in mind that out of some cities there is little or no reception on tmobile.
AB: Can't he roam on AT&T?
OP: What do you have now? Do you need a 3,000 minute plan? Is there a 2 year contract? What phones do you get, for how much, and do you want those phones?? etc. etc.
My point is, there are so many variables, so it's hard to say.