Strange idea but have you factory reset it and cleaned the sim card/sim slot?
Done both of these, and yes I suspect I've done some damage some how to the 3G aerial and/or chip.
Haven't been into a $G area to see if that will work..annoying, but as the Chassis had several cracks in it already, the phone wasn't going to last forever.
As i'm off to the US with work shortly, will see what prices are like over there, otherwise, will be on the hunt for a replacement.