I jail broke an iPhone 3GS and it modified the 'baseband'.

I jail broke an iPhone 3GS and the software modified the 'baseband' last year right before AT&T and Apple got their act together to allow official unlocking. I since have tried to restore the phone and although AT&T has officially unlocked the phone, I can't seem to get the phone back on AT&T. Do your have a part for the phone that could fix the 'baseband' issue or can I send it in to be fixed? Thanks.