Many iPhone 3GS users updated their iOS firmware to iOS 6.0 and found out that they have lost their unlock and stuck in recovery mode. At the time there is no untethered jailbreak solution available for iOS 6.0 firmware and no unlock solution available for iOS 6 baseband 5.16.07.
There is a way out to get rid of iOS 6.0 basband 5.16.07 by downgrading it to iOS 4.1 firmware baseband 5.13.04 which is unlockable and Apple is still sighing it. Its still possible to unlock your iPhone by updating the baseband to 6.15.00 and then downgrading to 5.13.04. Baseband 6.15.00 is an iPad baseband and in order to downgrade to 5.13.04 you will need to update 6.15.00 first. Unfortunately there is no direct way to downgade 5.13.04 at the moment.
If you have an AT&T iPhone 3GS, you can unlock it permanently by visiting AT&T official website and fill out iPhone 3GS unlock request form.
WARNING: If you own the new iPhone 3GS 8GB then don’t follow this guide. Othewise, by updating to the iPad’s 6.15.00 baseband, you will brick the chip and there’s no software fix available. check if your iPhone 3GS serial number is like this XX931XXX that means it was produced in 2009 in week 31 and it is safe to flash it with iPad baseband otherwise don’t follow this guide.
Unlock iPhone 3GS iOS 6 Baseband 5.16.07 By Downgrading To 5.13.04 Baseband
Part 1: Downgrade to iOS 4.1
1. Backup your contacts, photos, apps etc. Remove your SIM card.
2. Download iOS 4.1 firmware for iPhone 3GS from here.
4. Download latest version of TinyUmbrella from here.
6. Put your iPhone into DFU mode.
7. Launch iTunes, connect your iPhone, hold down the SHIFT for Windows or Option for Mac while you click the RESTORE button in iTunes and select the iOS 4.1 firmware file you have just downloaded. If you get an iTunes error 3194, read here on how to fix it.
8. The restore will end with error 1015 and recovery loop on the iPhone, this can be resolved using the “Exit Recovery” button in TinyUmbrella.
Part 2: Installing iPad baseband 6.15.00
9. Start redsn0w 0.9.6rc18.
10. Browse for the iOS 4.1 firmware you just downloaded.
11. Select ‘Install Cydia’ and ‘Install iPad Baseband’. Warning: installing iPad baseband will break your GPS, if you have the new 3GS made after week 28 of 2011, it does not support the iPad baseband. We will downgrade to 5.13.04 later for the GPS fix.
12. Follow on screen instructions to put your device into DFU mode to begin the jailbreak.
13. When the process is done, you will find that your iPhone is now jailbroken on iOS 4.1 with iPad baseband 6.15.00. To make sure you can always go back to iOS 4.1, launch Cydia and select ‘Make my life easier.’
Part 3: Downgrading to baseband 5.13.04 (GPS Fix)
15. Launch redsn0w. Go to Extras > Select IPSW button in redsn0w to point to the original firmware you downloaded in Step 2.
16. Do a controlled shutdown of your iPhone (“slide to power off”).
17. Return to the first screen and click ‘Jailbreak’. Check the ‘Downgrade from iPad baseband’ checkbox, uncheck Cydia and click Next.
18. Redsn0w will start doing the downgrade and you will see ‘Flashing Baseband’ screen on your iPhone with the Pawnapple icon. DO NOT INTERRUPT your iPhone while baseband flashing is in progress.
19. When done, your iPhone will reboot itself and you will now have iOS 4.1 with baseband 5.13.04 that can be unlocked with ultrasn0w.
20. You may want to update to iOS 5.1.1 which has untethered jailbreak and can also be unlocked with ultrasn0w 1.2.7. (it’s for baseband 6.15.00 but will work for any baseband). You can install iOS 5.1.1 only if you have the SHSH saved on Cydia or locally.
Part 4: Unlock with ultrasn0w
21. Launch Cydia from Springboard (home menu).
22. Search for ultrasn0w on Packages in Cydia. If you cannot find it, add new sources by typing ultrasn0w repo: repo666.ultrasn0w.com (with zero, not o).
23. Install Ultrasnow 1.2.7.
24. Reboot your iPhone.
25. Turn off 3G and insert your SIM card. It should pick up your mobile signal.
Note: At the time of writing, there’s still no ultrasn0w for iOS 6 so it will be pointless to update to iOS 6 for now.
via Beijing iPhone