These are instructions on how to jailbreak your iPhone 3GS on the 4.3.2 firmware using RedSn0w for Mac.
If you want to jailbreak a lower firmware version you can find the appropriate tutorial here.
Make sure not to update to iOS 4.3.2 if you need an unlock as one is not yet available unless you opt to use the iPad baseband.
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).
4. There are reports that 06.15 may disable your GPS. The iPhone Dev-Team is currently working on a fix.
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. If your baseband is already unlockable and you are on a lower firmware version then use PwnageTool to update to 4.3.2 without upgrading your baseband.
Step One
Create a folder on your desktop called Pwnage
Download RedSn0w from here and place it in the Pwnage folder. Likewise, download the latest 4.3.2 firmware from below and place it in the same folder.
4.3.2 (3GS): iPhone2,1_4.3.2_8H7_Restore.ipsw
Extract the RedSn0w zip file by double clicking it.
Step Two
Connect your iPhone to the computer and launch iTunes.
Select your iPhone from the list of devices on the left. Now hold down Option and click the Restore button. Restore is preferred as it won't create any wasted space on your iPhone.
Navigate to the Pwnage folder on your desktop and select the 4.3.2 firmware ipsw. Click the Choose button to continue.
Step Three
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.
Step Four
Once RedSn0w opens click the Browse button
