How to Downgrade iPhone 3GS 4.3.5 to 4.1 [Tutorial]

One of Limera1n blog readers was able to downgrade his iPhone 3GS from iOS 4.3.5 to 4.1 firmware. Let's check his simple guide to downgrade 4.3.5 to 4.1 after the jump.

Why to downgrade 4.3.5 to 4.1 iPhone 3GS?

As most of you know that iOS 4.3.5 only have tethered jailbreak which mean that you have to connect your iPhone 3GS to PC every time you reboot it. When you downgrade 4.3.5 to 4.1 iPhone 3GS you will be able to get untethered jailbreak.
Required downloads to downgrade 4.3.5 to 4.1 iPhone 3GS:

Download Ireb4.
Download - Part 1 - Part 2 - iOS 4.1 custom firmware (made by sn0wbreeze)
Download redsn0w 0.9.6 (mirror)
Download iTunes 10.4
How to downgrade 4.3.5 to 4.1 iPhone 3GS :

Step 1: Run Ireb4 , your iPhone 3GS will enter dfu mode.
Step 2: Go to iTunes and flash 4.1 custom firmware ipsw.
Step 3: Jailbreak your iPhone 3GS with Redsn0w 0.9.6b6 - follow

Step 4: Unlock your iPhone 3GS with ultrasn0w - follow

Here's the step by step guide:

STEP 1: Download redsn0w 0.9.6b5, iOS 4.2.1 for your device(download links at the end).

STEP 2: Update to 4.2.1 firmware using the IPSW file you just downloaded via iTunes 10.1.

STEP 3: Launch Redsn0w 0.9.6b5, and browse for iOS 4.2.1 firmware final version.

STEP 4: Now you have to select "Install Cydia" and "Install iPad baseband", and then click "Next" (in this step redsn0w will update your baseband to 06.15.00 which works with ultrasn0w 1.2)

STEP 5: Now make sure your device is both OFF and PLUGGED IN to the computer before you click “Next”.

STEP 6: At this stage you will need to put your iPhone in DFU mode by holding “Power” button and then while holding the “Power” button, you will now have to hold “Home” button too. Now after few seconds release “Power” button but keep holding “Home” button until installation begins.

STEP 7: You will Get a Jailbroken Device on the latest iOS 4.2.1 and the unlockable baseband 06.15.00

STEP 8: This step is only for these devices iPhone 4, 3GS (New Bootrom), iPod touch 4G, 3G, 2G, iPad. While this is tethered jailbreak and whenever you want to do anything related to jailbreak like SSH your device, or running Cydia, you must first run your device in the so called “jailbroken state” on every reboot by using “Just boot tethered right now” option.

Step 4: Unlock your iPhone 3GS with ultrasn0w - follow

Step 1: Open Cydia on your iPhone 4 or 3GS, Go to Manage->Sources