If you’re one of the many iPhone 3G or 3GS users who are not able to downgrade from 6.15.00 to 5.13.04 due to different variation of NOR chips used, the latest redsn0w might do the trick.
UPDATE: If you have an iPhone 3G or 3GS locked to AT&T, get the official unlock here.
In case you just found out about this, MuscleNerd came out with a method to downgrade baseband 6.15.00 to 5.13.04 that allows unlocking with ultrasn0w and restore the GPS functionality on iPhone 3G and 3GS. The previous version of redsn0w failed to downgrade many iPhone 3G/3GS’ baseband as it only supports the most ‘prevalent’ NOR chip. This latest version should address that issue.
I won’t need to write all the details here because you might have attempted to downgrade your iPhone 3G or 3GS already. However, do note that some of the steps have been slightly revised (thanks to Unlockboot.com for this):
- Connect your iPhone in normal mode, then click “Jailbreak” after redsn0w identifies its model and BB version (you needn’t pre-select the IPSW anymore).
- Choose the “Downgrade from iPad baseband” option (you needn’t worry about de-selecting Cydia anymore).
- Do a controlled “slide to power off” shutdown of your phone and proceed through the normal DFU ramdisk steps.
Once your baseband has been downgraded to 5.13.04, it’s highly recommended that you reinstall mobile substrate and ultrasn0w.
Those with iPhone 3GS made after week 28 of 2011 should not make any attempt to flash the baseband to 6.15.00 in hoping to downgrade to 5.13.04 because this will brick your baseband chip!
Good luck and let us know if it works for you this time!