How to restore your iPhone to 3.1.2 Options

[Link]

I'm going to show you the easiest way to restore your iPhone 3G or 3GS to 3.1.2, whatever version you're coming from!

Restoring/downgrading is great if you're stuck with an official release like 3.1.3 (which, at time of writing, cannot be completely jailbroken and unlocked) and want to go to 3.1.2. Or if you broke your jailbroken iPhone and need to restore.

I'm going to do this tutorial with steps. Occasionally, if I feel there's something that needs to be expanded on, I'll do that.

1. Download iPhone OS 3.1.2. Make sure it's the version for whatever phone you have (3G or 3GS). Due to copyright issues, I am unable to provide links, but this is usually easy to find. ModMyi has a large library of firmwares, just check if the selected one is compatible with your OS.
2. Open your hosts file, usually located in %SystemRoot%\system32\drivers\etc\. Add this to it:

CODE

74.208.10.249 gs.apple.com

This does a few things. Let me explain what gs.apple.com is. It's what iTunes contacts to see if you're eligible for upgrades and downgrades. Now, 74.208.10.249 is a server owned by Jay Freeman aka Saurik, who created Cydia. Now, when iTunes thinks it's contacting Apple, it's really talking to Cydia.

Restart iTunes after doing this.
3. Time to put your iPhone in DFU mode. This mode is the easiest for what we need right now. Plug in your iPhone to your computer. Hold down the lock (power) and home (menu) buttons for 10 seconds. Let go of the lock (power) button, but keep holding the home (menu) button. Once iTunes detects it, let go of the home button. The screen should be completely black! If your phone is displaying an iTunes logo with a USB cord, or an image of Steve Jobs swearing in Cyrillic, you're in Recovery mode and need to try again.


4. It's restore time. Hold down the Shift key (or Option key if you're in OSX) and click the Restore button. Browse to where you downloaded the firmware file, and select that file. Let iTunes do its thing, and restore any backups you may have.
5. Reopen your hosts file, and remove the line you added earlier, in step 2.

I hope this guide helped you, and was easy enough to read. Enjoy!

[Justin]

Oh. Two things.
1. That's actually not necessary for the 3G. It doesn't use SHSH's iirc.
2. Also note this won't work if you don't have 3.1.2 SHSH's on file (such as if your 3GS came with 3.1.3 or you've never opted into Saurik's on-file service).