I have Iphone 4 was at

How was your iPhone unlocked originally? When your iPhone

locked after restore, that indicates it was jailbroken or hacked

to work because if AT&T unlocked the iPhone it would still

be unlocked. Contact whoever unlocked it originally and ask

for their assistance. Or contact AT&T who now offers unlocking

if you meet their requirements.

It is not the wireless carrier's responsibility to warn you that the

update might lock your iPhone. You assumed responsibility when

the jailbreak was applied. Updates are written for and tested to work

with the normal software that is found on the iPhone, not for

software that was altered to perform functions not intended by

original OS and hardware combination. Carrier had no

knowledge the iPhone had been altered and therefore could not

warn you against possible locking.

Google may assist you in finding a solution, but these fora cannot.