Unlock iOS 4.3.1 on iPhone 4, 3GS Using Ultrasn0w

The newly released Sn0wbreeze 2.4b1 supports Ultrasn0w unlock for iPhone 4 and 3GS users (old basebands only) which otherwise happens to be broken on the latest iOS 4.3.1 firmware.
If you have jailbroken your iPhone 4/3GS (old basebands only) on iOS 4.3.1 using Sn0wbreeze 2.4b1, and you rely on an unlock, you can use Ultrasn0w to unlock your iPhone on this latest firmware so that you can use it on any carrier you like.

The following step by step instructions will help you jailbreak and unlock supported iPhone 4 and 3GS running on iOS 4.3.1. However before we proceed, please make note of the following:

• Sn0wbreeze 2.4b1 supports Ultrasn0w unlock for basebands (01.59.00 / 04.26.08 / 05.11.07 / 05.12.01 / 05.13.04 / 06.15.00)
• ultrasn0w is NOT compatible with the folllowing basebands (02.10.04 / 03.10.01 / 04.10.01 / 05.14.02 / 05.15.04)
• iPhone 3GS users can upgrade to 06.15.00 baseband now. Upgrading your iPhone 3GS baseband to the 06.15.00 iPad baseband hack to unlock MAY cause you to lose your GPS
• There is NO unlock for the stock iOS 4.3.1 yet. If your iPhone relies on a unlock, STAY AWAY from stock iOS 4.3.1.
• Sn0wbreeze is a tethered iOS 4.3.1 jailbreak for iPhone, iPad and iPod touch. 

Mac users follow the links below to jailbreak iOS 4.3.1 using PwnageTool:

• How to Jailbreak iOS 4.3.1 on iPhone 4 and iPad
• How to Jailbreak iOS 4.3.1 on iPhone 3GS (New and Old Bootrom)

Ultrasn0w 1.2 unlocking requires that your iPhone 3GS is jailbroken with 06.15.00 baseband.

Step 1: First up, you will have to jailbreak your iPhone 4 or 3GS using Sn0wbreeze 2.4b1. Instructions for jailbreaking iOS 4.3.1 using this new version of Sn0wbreeze are exactly similar to the last release. Simply download Sn0wbreeze 2.4b1, and then follow our detailed step by step guide posted here to jailbreak iPhone 4, 3GS, iPod touch 4G / 3G and iPad running the latest iOS 4.3.1 firmware.

Step 2: Once you are done with the jailbreak, you can now unlock your iPhone on the supported basebands using Ultrasn0w 1.2 from Cydia. To do this:

• Start “Cydia” on your iPhone.
  
• Touch on “Manage” tab on the bottom.
  
• Now touch on “Sources” as seen in the screenshot below:
  

Note: If you jailbreak your iPhone using PwnageTool on a Mac, add http://djayb6.com repo in Cydia and install “Ultrasn0w Fixer for 4.3.1” before installing "Ultrasn0w" as mentioned in the steps below.

• Touch on “Edit” and then on “Add”. You will be prompted to enter a url source as seen in the screenshot below. Type “http://repo666.ultrasn0w.com” and touch on“Add Source” to add this repo if you haven’t already.

Cydia will now automatically update your sources by following a series of automated steps.

• After installation is completed. Search for “ultrasn0w 1.2” in Cydia and install this application. This app will automatically unlock your iPhone so that you can use it with any carrier.

Step 3: Now simply restart your iPhone and you should now have a fully unlocked iPhone 4 or 3GS, running iOS 4.3.1

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