For iPhone 3GS Only: How to Update iPhone 3GS to 06.15.00 Baseband for Unlock: Ultrasn0w 1.2 unlocking requires that your iPhone 3GS is jailbroken with 06.15.00 baseband. Follow the complete guide posted here (with PwnageTool) or here (for Redsn0w) to update your iPhone 3GS baseband to 06.15.00 and jailbreak it on iOS 4.1 / 4.2.1 before proceeding with the following steps.
Step 1: Of course you need to jailbreak your iOS device before you can unlock it. The latest tool to jailbreak iPhone 4 or 3GS is Sn0wbreeze 2.3b4. You can download Sn0wbreeze 2.3b4 from here, and check out our step by step guide posted here for jailbreaking iPhone 4, 3GS, iPod touch 4G / 3G and iPad on the latest iOS 4.3 firmware.
Step 2: After jailbreaking, to unlock your iPhone on the supported basebands using Ultrasn0w, follow these steps.
Find the “Cydia” app on your iPhone and tap to run it.
Once Cydia is running, tap on “Manage” tab.
In Manage, there will be three options as shown in the screenshot below. Just tap on “Sources”.
Now tap “Edit” and then “Add”. A popup like prompt (that is shown in the screenshot below) will open. Here type: “http://repo666.ultrasn0w.com” and tap on“Add Source”. This will add a repository in Cydia that contains Ultrasn0w. Wait while Cydia performs the update.
When Cydia is done with adding resources. Go to search and type “ultrasn0w 1.2”. Install this application and your iPhone will get unlocked automatically.
Step 3: A reboot is required to make the unlock work. Restart your iPhone and it will boot into an unlocked state. Enjoy!
Mac user? no problem. We have already covered extensive tutorials on how to jailbreak iOS 4.3 using PwnageTool: