FYI it doesn't matter if you are roaming. T-Mobile offers free nationwide roaming so you don't get charged for it. Actually, Sprint does the same thing, so I would imagine that unless you are on some regional plan, this will be the same regardless of what carrier you are with. If you signed up with T-Mobile after Oct 25 2009, then regional plans don't even exist, so that won't be a problem either.

I had perfect reception in Missouri and also Indiana. Haven't tried elsewhere with this carrier though.