Unlock iPhone 3GS iOS 6.1 Baseband 5.16.08 By Downgrading To 5.13.04: Many iPhone 3GS users updated their iOS firmware to iOS 6.1 and found out that they have lost their unlock and stuck in recovery mode. At the time there is evasi0n untethered jailbreak solution available for iOS 6.1 trough 6.0 firmware and no unlock solution available for iOS 6 baseband 5.16.08.
There is a way out to get rid of iOS 6.1 basband 5.16.08 by downgrading to iOS 4.1 firmware’s baseband 5.13.04 which is still unlockable and Apple is still sighing it. It’s still possible to unlock your iPhone by updating your baseband to 6.15.00 and then downgrading to 5.13.04. Baseband 6.15.00 is an iPad baseband and to downgrade to 5.13.04 you will need to update 6.15.00 first. Unfortunately there is no direct way to downgrade 5.13.04 at the moment.
If you have an AT&T iPhone 3GS, you can unlock it permanently by visiting AT&Tofficial website and fill out iPhone 3GS unlock request form.
WARNING: If you own the new iPhone 3GS 8GB then don’t follow this guide.
How to Unlock iPhone 3GS iOS 6.1 Baseband 5.16.08 by Downgrading to 5.13.04:
Part 1: Downgrade to iOS 4.1 firmware
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. Now 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 could 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.
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 could be unlocked with ultrasn0w 1.2.8.
Part 4: Unlock iPhone 3GS iOS 6.1 Baseband 5.13.04 with ultrasn0w 1.2.8
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 1.2.8 and reboot your iPhone.
24. Now turn off 3G and insert your SIM card. It should pick up your mobile signal.
Part 5: Update to iOS 6.1 by Preserving your Baseband and then Unlock with Ultrasn0w (Fixer).