Download Ultrasn0w 1.2.1 to Unlock iOS 4.3.1 on iPhone 4, 3G & 3GS [How to Guide]

By on April 10, 2011

You can Download Ultrasn0w 1.2.1 which has just been released by iPhone Dev Team to unlock iOS 4.3.1 on iPhone 4/3G/3GS running on the old baseband. It is an updated version of Ultrasn0w 1.2 that also brings some major fixes especially a fix for annoying signal bar issue.

Ultrasn0w 1.2.1-Unlock-iphone 4-3G-3GS It should be kept in mind that Ultrasn0w 1.2.1 is only an update (not the new one) and can’t unlock the iPhones with newer basebands .It only fixes the compatibility and the signal bar issues on the current devices which has been jailbroken on 01.59.00 / 04.26.08 / 05.11.07 / 05.12.01 / 05.13.04 / 06.15.00 preserved basebands using PwnageTool or Snowbreeze 2.5.1.

We’ve pushed out the 4.3.1 compatibility fix for ultrasn0w in Cydia — it’s now at version 1.2.1. If you’re not already at 4.3.1 and you need the unlock,please be sure you understand how to get to 4.3.1 using a custom IPSW that doesn’t update your baseband.
This isn’t a new unlock! It’s to allow those who are already unlocked to use FW 4.3.1. It also fixes the signal bar issue for those who aren’t using the unlock but retain an older baseband intentionally.
AFTER INSTALLING ULTRASN0W 1.2.1, PLEASE REBOOT YOUR iPHONE using the normal “slide to power off” swipe. T-Mobile users in the USA also should disable 3G mode in Settings->General->Network.

An Alert for iPhone 3GS Only:

Ultrasn0w 1.2.x unlocking only works if your iPhone 3GS is jailbroken with 06.15.00 baseband. You can follow the complete Redsn0w 0.9.6b5 tutorial  to update your iPhone 3GS baseband to 06.15.00 and jailbreak it on iOS 4.1 / 4.2.1 prior to go ahead with following tutorial. It should also be noted that updating iPhone 3GS baseband to iPad’s 06.15.00 might result in loss of GPS functionality too.


Firstly, download Sn0wbreeze 2.5.1 and then Jailbreak your iPhone 4/3GS on iOS 4.3 tethered with Sn0wbreeze 2.5.1.


After jailbreaking it, you can unlock your iPhone 4/3GS on basebands listed on the top of this post using Ultrasn0w 1.2.


Launch “Cydia on your iPhone 4/3GS.

Open “Manage” tab.


Then open “Sources” as shown below;

iPhone 4-3GS Unlock-Ultrasn0w


Open “Edit” & then tap on “Add”.


Put in URL box and touch on “Add source”.

iPhone 4-3GS Unlock-Ultrasn0w


Cydia will automatically update your sources. Just relax and wait for next step patiently.


Now start Cydia, search for “Ultrasn0w 1.2.1” and install it.

New Ultrasn0w 1.2.1 Unlock-iPhone 4


Restart your iPhone 4/3GS to finalize the whole process.

Congratulations! You have done the job successfully. Now you can use your iPhone 4/3GS on iOS 4.3 with any carrier since it has been unlocked.


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