IMPORTANT FOR UNLOCKERS
During this process you can update your baseband to the 06.15 version. If you are on 05.14 or 05.15 or higher you will need to do this to unlock. You do not need to do this for jailbreak only. Please read the following very carefully before deciding whether to do this. You can find out baseband version here.
1. There is no way to come back down from 06.15, and there’s no hiding the baseband version from Apple. You’ll be voiding your warranty in a very obvious way.
2. If some future baseband comes out with a critical fix, you won’t be able to update to it if it remains down in the 05.xx sequence (then again, you wouldn’t update to it if you wanted to keep your unlock anyway).
3. Starting with FW 4.2.1 if you have 06.15 on your iPhone you won’t ever be able to restore to stock firmware (it will fail). You’ll need to only restore to custom IPSWs (then again, if you’re unlocker you should already be doing that).
Don’t update to 06.15 if you don’t need to! Only do this if you need the unlock and you’re stuck on 05.14 or 05.15, and you’re willing to assume the above risks.
Create a folder on your desktop called Pwnage
Download RedSn0w from here and place it in the Pwnage folder. Likewise, download the latest 4.2.1 firmware from below and place it in the same folder.
4.2.1 (3GS): iPhone2,1_4.2.1_8C148a_Restore.ipsw
***If you are already on iOS 4.2.1 you can skip this step. If you are on an unlockable baseband and on a lower firmware you should use PwnageTool instead to update without upgrading your baseband.
Once iTunes has finished updating your iPhone to the desired firmware open the Pwnage folder on your desktop and launch the redsn0w application from the redsn0w folder we extracted earlier.
You will be asked if this device is a newer fixed model. If yours is then click the Yes button; otherwise, click the No button. At this time you can only perform an untethered jailbreak on the older model.
Verbose boot displays detailed information on boot of your device and is generally only needed by developers and advanced users.
Make sure Cydia is selected. For this tutorial we will also select Custom boot logo and Custom recovery logo.
*Remember the rules for boot logos are: RGB or Grayscale format with Alpha channel and dimension below 320×480. If you would like to use the iClarified ones they can be found here: Boot Logo, Recovery Logo
RedSn0w will now guide you through the steps to get into DFU mode. You can find more help with DFU mode here
Once this is complete you will be notified that RedSn0w is done. Click the Finish button. When your iPhone finishes rebooting (5 minutes or so) it will be jailbroken with Cydia on the SpringBoard.
If you have problems with RedSn0w on Windows Vista or Windows 7. Right click the executable and set it to run as administrator in Windows XP compatibility mode.
If you have a newer iPhone 3GS and performed a tethered jailbreak you can use Redsn0w to help you boot back into your jailbroken device. Simply select Just boot tethered right now from the options window and click Next.
Follow this tutorial to unlock your device if you updated to the 06.15.00 baseband.
*As usual a big thanks to the iPhone Dev-Team for their hard work and contribution to the iPhone community.