Iphone 3GS 4.3.4 Unlock

[ayveoh]

Hey guys, my friend gave me a ATT Iphone 3GS (5.16.02, 4.3.4) that they "found" I know I can do a tethered jailbreak, but is it possible to unlock it for T mobile?

Is it possible to downgrade to a earlier firmware and then jailbreak?

Model number is MB715LL if that gives you a hint on how old the iphone is, because I don't know the history of it. If it has ever been jailbroken or not.

It just says no sim at the top.

Thank you.

[iYeow]

Put iphone into dfu mode
Restore to 4.1
Exit recovery to kick out error 1015.
Run Redsn0w to install cydia , rerun again to update to ipad bb

[ayveoh]

I cannot exit recovery mode, used recboot and tiny umbrella and holding down both home/power