Some users have been reporting issues when trying to unlock their iPhone on iOS 5.1. Since Ultrasn0w has not been updated yet, you must install the ultrasn0w 5.1 fixer through cydia. But that alone still leaves some users with out an unlock, especially iPhone 3GS users with the 06.15.00 baseband. Worry no longer, there is a solution. I have personally tested this method today so I can give you 3GS users with the 06.15.00 my word.
The first thing you will need to do is to restore your iPhone 3GS with a custom firmware created by snowbreeze. I have already made a post on that process so please FOLLOW THAT GUIDE HERE and when you have finished that process come back here and start on step one.
Note: If Ultrasn0w is installed uninstall it before you proceed.
Step 1: Launch Cydia and select the ‘Manage‘ tab from the tool bar at the bottom of the application. Select ‘Sources’ from the resultant list.
Step 2: Tap the ‘Edit‘ option in the top right hand corner of the screen before selecting the ‘Add‘ button on the left hand side of the tool bar.
Step 3: In the pop up alert view enter the repository URL which is ‘http://repo.iparelhos.com‘, then press ‘Add Source‘.
Step 4: After the repository has refreshed and finished loading sources, tap on the repo name in the sources list which will display the Ultrasn0w Fixer utility.
Step 5: Select the Fixer utility, pressing ‘Install‘ in the top right hand corner. Confirm the installation and then wait for the process to be completed.
Step 6: Now that the Fixer package is complete, the current Ultrasn0w 1.2.5 software needs to be installed. Select the ‘Search’ option from the bottom of Cydia, typing in ‘Ultrasn0w‘ and hitting the ‘Search‘ button.
Step 7: When the Ultrasn0w tool appears, select it from the table and then select ‘Install’ as per step 5.
Step 8: Download the latest version of redsnow.
Step 9: Download the iPhone 3GS iOS 5.1 Firmware.
http://www.felixbruns.de/iPod/firmware/ – Search for it from the second drop down menu.
Step 10: Open redsn0w=>Click Extras=>Select IPSW=> Select the 5.1 iPSW you just downloaded
Step 11: Click Back=>Click Jailbreak=>Click Next=> Proceed to put your device into DFU mode by following the instructions on screen.
Step 12: After redsn0w has recognized you device in DFU mode make sure you have the Jailbreak check box checked AND the install iPad baseband checked. Then hit next. (REMEMBER, YOU CAN ONLY INSTALL THE IPAD BASEBAND IF THE 3RD 4RTH AND 5TH DIGIT OF THE SERIAL NUMBER ARE LOWER THAN 135 OR IN THE 900′S)
Step 13: Since this is a tethered jailbreak you will have to boot tethered. Open redsn0w again=>Click Extras=> Click Just Boot=> Hit next and put your device into DFU mode. Your iPhone should then reboot normally.
When your phone reboots, your phone should be properly unlocked now. Finally.
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