How to Downgrade from iOS 4.0 to OS 3.1.2.

WOOHOO!! I was doing the stardard method to downgrade my iPhone3GS to OS 3.1.2 from iOS 4.0 when IT CRASHED!!!
Keeps giving the 1015 ERROR!!

Thankfully I remained calm by jumping up and down the walls of my room, i found a solution! (did alittle googling of cos xD)

Preparation:
Download OS 3.1.2 IPSW file and Redsn0w.
Files are provided below.

Its crucial that you follow these steps EXACTLY!

Here are the steps:

1. Right-click on to Notepad and select Run as Administrator.
2. Open the file C:\Windows\System32\drivers\etc\hosts (Windows) or /etc/hosts (Mac OS X) and add the following entry to the bottom of the file.
74.208.10.249 gs.apple.com



Restore
———-
3. Connect your iPhone to the USB and put it into DFU mode. iTunes will display an alert stating you need to restore your device, click ok then on Mac: Hold option + click restore, on Windows: Hold Shift + click restore and navigate to your previously downloaded 3.1.2 FW.

4. After the restore finishes you should be hit with a 1015 error. That’s expected. Your phone should be in Recovery mode now and iTunes will tell you to restore again. Click OK then hold option + click on restore again – this time you do not have to go into DFU mode – and navigate to the 3.1.2 FW.

Jailbreak
———–
5. After the restore finishes again it’ll throw another 1015 error. That’s expected again. This time, just select OK and close iTunes. Open Redsn0w 0.9.4 and jailbreak as normal. Uncheck all the ticks while jailbreaking.

6. After the jailbreak is finalized your device should reboot and strange enough you successfully downgraded to 3.1.2.

-by Kamrul (edited by Me)

Redsn0w:

• Windows (Mirror)


• Mac OSX (Mirror)

OS 3.1.2:

• iPhone3G


• iPhone3GS


• iPodtouch3G