This jailbreak and unlock will work for iPhone 3G or iPhone 3GS with baseband 04.26.08, 05.11.07, 05.12.01, or 05.13.04. It will also work with iPhone 4 with baseband 01.59.00.
But what happens if you’re not on one of those basebands? Depending on your phone model and configuration, you might have to update the baseband to 06.15.00, which is fully unlockable, then unlock using UltraSn0w.
Let's jailbreak!
Step 1: Make sure you have the latest version of iTunes installed on your computer. If not, update iTunes.
Step 2: Make sure you have iOS 4.2.1 on your iPhone 3G or 3GS.
Step 3: Download RedSn0w 0.9.6 beta 5 as well as iOS 4.2.1 for your iPhone 3G or 3GS from our downloads section.
Step 4: Launch RedSn0w and browse for the iOS 4.2.1 firmware you downloaded in the previous step.
Done, your iPhone is successfully running a jailbroken iOS 4.2.1, and we have updated the baseband to 06.15.00.
If your device is an iPhone 3GS with old bootrom, you won’t have any problem after that. If however it is a newer bootrom, you will notice that you iPhone shows the “connect to iTunes” logo every time you reboot it. It’s normal. While very inconvenient, it’s the way it is.
To go around that, launch RedSn0w, plug your iPhone in and select “just boot tethered” just like the image below. It will kick boot your iPhone.
How to Unlock Your 4.2.1 iPhone 3G or 3GS
Step 1: Launch Cydia, and search for UltraSn0w.
Step 2: Download UltraSn0w.
Step 3: Reboot your iPhone.
That’s all! Watch your Phone bill!
Stay tuned for more!