I would try restore then rejailbreak. Its highly likely that the problem does not lie in the firmware. I remember when I first got a 4gb iphone back in the day I encountered a similar problem full bars.. then all of a sudden no service, the phone would only have signal for a minute or two every time.
Yeah, thats not T-Mobiles problem, thats a glitch with the iPhone.
Just have a spare phone on hand and when it happens, put the sim card in another phone, gain service, and be sure to log onto a web page so you will regain your Edge.