My elder lad has a G1 and absolutley loves it. He has not had any of the problems you describe, and I must say that it does rather sound like it is a problem with the handset itself rather than the T-Mobile network. Our coverage is superb (the nearest transmitter is less than 200m away hence the lack of need for heating in this house) but he does work in marginal areas without anything like what you've described.

Return for exchange perhaps?