Downgrade Iphone 3G(s) 3.1.3 firmware to 3.1.2 firmware

In case you have accidentally (or not) upgraded your Iphone 3G(s) to 3.1.3 firmware, you can downgrade it to 3.1.2 firmware and jailbreak it provided that you have signature hashes of your Iphone (SHSH) on Cydia (Saurik’s server).

This post will help you to downgrade to 3.1.2, but you may not have service on your Iphone after downgrading to 3.1.2. In order to get service, follow instructions in this post. Don’t forget to change your /etc/hosts file in OS X (or equivalent file under windows) and add this line: 74.208.10.249 gs.apple.com. This will yell iTunes to authenticate 3.1.2 firmware upgrade (or downgrade in this case) on Cydia’s server and not on Apple’s server. Without this change you’ll get an error and you’ll not be able to start firmware downgrade. After this, install afc2add package in Cydia which will fix directory structure of your Iphone which has changed with 3.1.2 firmware.

To setup tethering on your Iphone, follow this post. I was able to get quite good download speed while tethering on my Iphone 3Gs. Speed test was done on Speakeasy’s DC servers:

Iphone 3Gs tethering speed

Iphone 3Gs tethering speed

Download Speed: 2783 kbps (347.9 KB/sec transfer rate)
Upload Speed: 292 kbps (36.5 KB/sec transfer rate)

Here you can read how to put your phone to recovery and DFU modes. Finally, all firmwares necessary to perform above tasks you can find here.
After upgrading to 3.1.3 firmware you’ll loose (for now) ability to unlock your phone, which is also true after you downgrade from 3.1.3 firmware to 3.1.2 firmware.

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