Were you able to get your e-mail working? It sounds like you've done quite a bit of troubleshooting. I Iooked into this, but did not find much helpful information on GeveySIM-email timeouts. When you tested the alternate APNs, did you also adjust all other settings? Although T-Mobile does not guarantee functionality of non T-Mobile devices, I hope we can get this working for you.
Hope this helps!
Thank you for your response. I have made all the changes to my settings, and tried several APN's. My Phone is jailbroken with Gevey, on 4.3.3 of iOS, stock 4.10.01 baseband. Anyway, what I found was that if I added this really long proxy string after the 8080, T-mobile works fine for internet and wifi, if not a little slow. When my T-mobile network is availabel the carrier automatically switches networks to AT&T. My T-Mobile phone still works, and sometimes my data still works, but email will not. I think this is a problem that has something to do with the area I live and the coverage here.