Apple has recently released firmware 3.1.3 update. There aren't many changes in this latest firmware from previous 3.1.2 firmware, but still people are quite eager to upgrade their iPhone/iPod Touch to firmware 3.1.3. The ones who are on official carriers can off course upgrade without any worries, but upgrading to latest firmware isn't a good idea for those who are using jailbroken/unlocked iPhone or iPod Touch. We warned jailbreak users NOT to upgrade to latest firmware as well, as doing so will alter baseband of their device can lose unlock capability. OS 3.1.3 contains a baseband update 05.12.01 for iPhone 3G and 3GS. The latest Modem Firmware 05.12.01 baseband is not down gradable. So if you accidentally updated your iPhone 2G, 3G, 3GS to OS 3.1.3 and you want to downgrade/revert it back to OS 3.1.2, this guide will help you to do so.

Couple of jailbreaking/unlocking tools for firmware 3.1.3 have emerged, including redsn0w 0.9.4 and sn0wbreeze 3.1.3, both of these tools are basically for jailbreaking iPhone/iPod Touch on firmware 3.1.3 anf they work as well. Problem is, they are not meant for all devices (iPhone 2G,3G,3GS and iPod Touch), also they work on Old Bootroms/Old device models only, so we again recommend to wait for a tested tool that works for jailbreaking and unlocking all iPhones/iPod Touch.

NOTE: This process will not downgrade your baseband, only your firmware will be downgraded.

Steps to Downgrade from iPhone 3.1.3 to 3.1.2

1. Install latest iTunes, click here to download if you don't have it. Now connect your iPhone to your computer.
2. Now you need to put your iPhone into DFU mode with following instructions:

* Connect your iPhone to your computer.
* Turn iPhone off.
* Hold power and home together for 10 seconds (exactly).
* Release power but keep holding home until the computers beeps (observed on a PC) as a USB device is recognized.
* A few seconds later iTunes should detect your iPhone.
* If the Restore Logo is present on the screen, you are in Recovery Mode, not DFU.

3. Once your device is in DFU mode, you will see a message on iTunes stating "iTunes has detected an iPhone in recovery mode". Click "OK", Now hold Option key while clicking Restore in iTunes and browse the 3.1.2 firmware for your iPhone 2G, 3G. You can download 3.1.2 custom IPSW file from here. Restore process will take around 10 to 15 minutes.

NOTE: If you encountered an error message like 1011, 1013, 1015, just ignore them.

4. Now your iPhone should be on firmware 3.1.2.

Disclaimer: Please try this at your own risk! Although this is a tested procedure, but still it's a workaround.

Please visit here and here respectively for complete coverage on jailbreaking and unlocking iPhone 3.1.3 firmware.

[via ihackintosh]