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I am a windows user and I have no access to a mac, so I downloaded a custom firmware (iPhone1,2_3.1.2_7D11_custom_Restore.ipsw). It is 239 MB. Is that about right for a 3g custom firmware? I am an ATT user and no need to unlock. Finally, do I just put my phone in DFU mode then shift-restore in iTunes and I should be good to go? Sorry for my noobness.

More details needed. What OS are you currently on? Are you jailbroken now?
 
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