Where can I download 4.x firmware files for the iPhone 3G?
Apple's iPhone 3G shipped with the iPhone 2.0.0 operating system and runs firmware version 4.x with some limitations. On your computer, right-click the link below to download the official firmware restore file.
iPhone 3G firmware version 4.0.0 can be found here: iPhone1,2_4.0_8A293_Restore.ipsw
iPhone 3G 4.0.1: iPhone1,2_4.0.1_8A306_Restore.ipsw
iPhone 3G 4.0.2: iPhone1,2_4.0.2_8A400_Restore.ipsw
iPhone 3G 4.1.0: iPhone1,2_4.1_8B117_Restore.ipsw
iPhone 3G 4.2.1: iPhone1,2_4.2.1_8C148_Restore.ipsw
Apple has announced that iOS firmware versions later than 4.2.1 will not be supported on the iPhone 3G hardware.