These are instructions on how to untethered jailbreak your iPhone 4, 3Gs on the 4.3.3 firmware using RedSn0w for Windows. The Mac version of this tutorial is here.
Make sure not to update to iOS 4.3.3 if you need an unlock as one is not yet available!
IMPORTANT FOR UNLOCKERS FOR 3Gs USER
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.
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 4.3.3 without upgrading your baseband.
Step One
- Download RedSn0w from here or here
- Download iOS 4.3.3
* 4.3.3 (3GS): iPhone2,1_4.3.3_8J2_Restore.ipsw
* 4.3.3 (4 GSM): iPhone3,1_4.3.3_8J2_Restore.ipsw
Extract the RedSn0w zip file.
Step Two
Launch the redsn0w application from the redsn0w folder we extracted earlier. 
Step Three
Once RedSn0w opens click the Browse button and Select the 4.3.3 firmware ipsw then click Open.
Step Four
Once the firmware has been verified click the Next button to continue.
Step Five
RedSn0w will now prepare the jailbreak data 
Step Six
From this window you can select the jailbreak options you would like.
Make sure Cydia is selected and click the Next button to continue.
Step Seven
Please plug your iPhone into the computer and make sure its OFF then click the Next button
Step Eight
RedSn0w will now guide you through the steps to get into DFU mode.
Hold down both the Home button and the Power button for 10 seconds. 
Release the Power button and continue holding the Home button until RedSn0w detects the device. 
Step Nine
Your iPhone will now reboot
Step Ten
RedSn0w will then begin uploading the new RAM Disk and Kernel.
Step Eleven
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.
*As usual a big thanks to the iPhone Dev-Teams, Geohot, and I0n1c for their hard work and contribution to the iPhone community.
**Windows 7 users can try running RedSn0w as an administrator in Windows Vista or XP compatibility mode if you experience any difficulties.
