How to jailbreak and unlock iPhone 3GS firmware by downgrading it from 3.1.3 to 3.1.2



A lot of users upgraded their iPhone 3GS firmware from 3.1.2 to 3.1.3 without knowing the consequences. So, if you want to jailbreak and unlock it using blackra1n, you’ll have to downgrade to 3.1.2 but the modem firmware will still be 05.12.01. Remember, before trying this out, back up your data. If you end up bricking your iPhone, I won’t be responsible for it. ( Credit for this guide goes to Cliff who sent it in! )

  1. Uninstall iTunes 9.0.3 to from your computer. Remember to back up your data, and rename the iTunes library folder to something else.
  2. Download and install iTunes 8.2.1. Download 3.1.2 firmware to your computer. ( links at the end of this post ).
  3. Connect your phone to the computer and hold shift and click restore in iTunes. Select the 3.1.2 firmware file.
  4. The restore might get stuck and you’ll get an error 1015 message.
  5. Ignore it and reboot your iPhone using the power + home buttons.
  6. You’ll now see the USB and iTunes logo on the iPhone display. This means that firmware 3.1.2 is installed. But right now, the phone is stuck in a DFU loop.
  7. To fix this, you’ll need to use iRecovery.
  8. Once you’re out of the DFU loop, iTunes will ask you to sync with the old backup. We suggest you avoid that and opt to set up a new phone. iTunes will reactivate your iPhone.
  9. Follow our guide on how to jailbreak iPhone 3GS with OS 3.1.2 with blackra1n RC3.
  10. You can now unlock your iPhone using blackra1n RC3. Follow this guide for instructions.

If you are running into issues, follow this guide to jailbreak and unlock your iPhone 3GS.

If you are using iPhone 2G, 3G, iPod Touch 1G or 2G ( non-MC models) follow this guide to jailbreak OS 3.1.3 with redsn0w.

Download iTunes 8.2.1 (32 bit)

Download iTunes 8.2.1 (64 bit)

Download iPhone 3GS OS 3.1.2

Update: Use this guide to jailbreak iPhone 3G/3GS with OS 3.1.3/3.1.2 untethered! ( no unlock yet, though)

Note: This method doesn’t work anymore. follow this guide to jailbreak and unlock your iPhone 3GS.