Apple released an upgrade to its iOS 5 operating system, on 7 March, along with the release of the new (third-generation) iPad. In the process, Apple not only broke exploits built into Redsn0w (for A4 Devices), Corona (A4 Devices) and Absinthe (for iPad 2 and IPhone 4S) jailbreak tools but also wiped out software unlocks for the iPhone 3GS and the iPhone 4, known as Ultrasn0w.

Users banking on jailbreaks to unlock their iPhones to work on multiple carrier networks will find themselves in turmoil once again, thanks to the new firmware update on iOS 5.1. The danger lies in the fact that upgrading to iOS 5.1 will also update the device's baseband, removing the effectiveness of the Ultrasn0w unlock tool.

In a recent official blog release, the iPhone Dev-Team have already warned users against blindly updating to iOS 5.1. The team advised users to use a custom IPSW before updating, if they wished to continue using Ultrasn0w on their devices.

Meanwhile, the Dev Team announced that Ultrasn0w itself would be updated to 5.1 over the next few days. The promised update will not, however, bring any added baseband support.

According to Redmond Pie, the update will enable unlocking only on devices and basebands which are supported by the 1.2.5 version of the tool. The currently supported baseband models include 01.59.00, 04.26.08, 05.11.07, 05.13.01, 05.12.01 and 06.15.00. Users can verify the baseband model by navigating to Settings > General > About > Modem Firmware.

For those users who can't wait for the latest public release of the Dev Team, a developer known as zmaster comes to the rescue.

The developer has released an interim fix on his own repository that goes by the name "Ultrasn0w Fixer". The users of devices running iOS 5.1 can install the package and then install the current version of Ultrasn0w to get the required unlock as long as the device and baseband are supported.

Users must note that their iPhone has to be jailbroken on iOS 5.1 using custom firmware with the old baseband preserved. For more information on how to jailbreak iOS 5.1 (tethered) using Redsn0w, click here.

Step 1: Since Ultrasn0w Fixer is not in a default repo, users need to add it. To do this, launch Cydia, select "Manage" from the tool bar at the bottom and then select "Source" from the ensuing list

Step 2: Tap on "Edit" and then select "Add"

Step 3: In the pop-up alert view, enter the repository URL - and hit "Add Source"

Step 4: After the repo is done loading, search Cydia for Ultrasn0w Fixer. Locate it and install it like a regular package

Step 5: Once the Fixer package is complete, install the latest version of Ultrasn0w (1.2.5). Since it is in a default repo, you need to search for it in Cydia

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