I just switched over to T-Mobile from Sprint and couldn't be happier. I have only taken a few trips since I got the new phone but calls seem clearer and service has been more consistent.

I second and third the comments above about using Amazon to buy your phone - I got mine there thanks to comments on FT along with a $250 rebate that was $75 over the cost of the phone. A very good deal that covers much more than just the activation fee. ^