If your iPhone 4 is on 01.59.00 baseband, then you are lucky. Ultrasn0w 1.2.1 could unlock it on iOS 4.3.1. Then some of you will be thinking why we can’t unlock it with Ultrasn0w 1.2 instead of 1.2.1. The newer version of Ultrasn0w was released in order to fix the signal bar issue after unlocking. If you use the previous version, you can’t find any signal bar on your phone.

 

Now, let’s proceed to the work of unlocking iPhone 4 on iOS 4.3.1 :

1. Jailbreak your iPhone 4 on 4.3.1 iOS using Sn0wbreeze on Windows or PwnageTool on Mac.

Guide: How to Use Sn0wbreeze 2.5 (Just use Sn0wbreeze 2.5.1 instead of 2.5)

Guide: How to Use PwnageTool 4.3

2. Open up Cydia.

3. Select the Manage tab at the bottom.

4. Tap on the edit button and then on the add button.

5. Then add this repo : http://repo666.ultrasn0w.com.

Unlock iPhone 4 4.3.1 iOS

6. The search for ” Ultrasn0w 1.2.1 ” in Cydia.

Unlock iPhone 4 4.3.1 iOS

7. Install the app.

8. Reboot your iPhone.

Unlock iPhone 4 4.3.1 iOS

That’s it! You’ve unlocked iPhone 4 on iOS 4.3.1.

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