IOS 4.2.1 Unlock for Iphone 3Gs and 3G (update)

Redsn0w 0.9.6b5 has just been released which can jailbreak and update iPhone 3GS & 3G baseband to 06.15.00 so that it can be unlocked using the newly released Ultrasn0w 1.2.
The new redsn0w 0.9.6beta5 is out. It gives both and OSX users the ability to flash the iPad 06.15 baseband on iPhone3G or iPhone3GS. It fetches the baseband files directly from Apple for now (the only IPSW you ever point it at is the stock IPSW for the FW on your iPhone right now). There may be a long delay while it’s doing this (their servers are getting pounded right now)
If you do flash your baseband via redsn0w, please keep it plugged into USB the whole time. You don’t want your battery to die during the flash process!
WARNING:
YOU DO THIS AT YOUR OWN RISK! PLEASE UNDERSTAND THE CONSEQUENCES OF UPDATING TO 06.15.
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.
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).
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).
Also, like the previous version of Redsn0w:
This version of Redsn0w is based on Geohot’s Limera1n bootrom exploit which has already pwned all current iOS devices for life. The only problem is that it is a tethered jailbreak, which means you will have to boot it into a “jailbroken state” on every reboot. This so called tethered or semi-tethered jailbreak condition in Redsn0w 0.9.6b4 & b5 however only applies to the new devices like: iPhone 3GS (new bootrom), iPhone 4, iPad, iPod touch 2G (MC Model), iPod touch 3G and the iPod touch 4G. Old devices like iPhone 3GS (old bootrom), iPhone 3G and iPod touch 2G (Non-MC Model) can be jailbroken-untethered right now using this latest version of Redsn0w. So until and unless Comex of Spirit and JailbreakMe fame comes up with another untethered hack for iOS 4.2.1, the jailbreak we get for the newer devices will be tethered (or semi-tethered).
Note: This release of Redsn0w is mainly targeted for iPhone 3GS & 3G users on iOS 4.1 / 4.2.1 who rely on a carrier unlock. All iPhone 4, 3GS, iPad and iPod touch users who don’t rely on a carrier unlock should follow the instructions posted here to jailbreak their iOS device on iOS 4.2.1 using Redsn0w 0.9.6b4.
Follow the instructions posted below to update your iPhone 3GS or 3G to 06.15.00 baseband and jailbreak it on iOS 4.1 /4.2.1.
Step 1: Download iOS 4.2.1 for iPhone 3GS or 3G.
Step 2: Update/Restore to iOS 4.2.1 firmware using the IPSW file you just downloaded via iTunes 10.1.
Step 3: Start Redsn0w 0.9.6b5 and point it to iOS 4.2.1 firmware to proceed with the jailbreak.


Step 4: Now select “Install Cydia” & “Install iPad baseband” options and then click “Next” to continue. Redsn0w will now fetch the exploitable 06.15.00 baseband from 3.2.2 important
and will replace it the baseband in iOS 4.2.1 / 4.1.

Note: Install iPad baseband option is applicable to iPhone 3GS & 3G users only who rely on a carrier unlock.
Step 5: Now make sure your device is both OFF and PLUGGED IN to the computer before you click “Next”.

At this stage you will be presented with a screen where you will have to quickly hold “Power” button and then while holding the “Power” button, you will now have to hold “Home” button too. Now after few seconds release “Power” button but keep holding “Home” button until installation begins.

Step 6: Sit back and enjoy while Redsn0w will do all the rest for you. Once done, your iPhone or iPod touch will restart automatically and you will find it jailbroken on the latest iOS 4.2.1 firmware, with the unlockable 06.15.00 baseband.
For iPhone 4, 3GS (New Bootrom), iPod touch 4G / 3G / 2G, iPad ONLY:
Step 7: Now from here onwards, whenever you want to do anything related to jailbreak like SSHing into your device, or running Cydia, you must first run your device in the so called “jailbroken state” on every reboot by using “Just boot tethered right now” option in Redsn0w.

How to Unlock iPhone 3GS & 3G on iOS 4.2.1 / 4.1
Follow the complete step by step guide posted here to unlock your iPhone 3GS and 3G on 06.15.00 baseband, running iOS 4.2.1 or 4.1 with Ultrasn0w 1.2.
UPDATE: Video instructions for the above tutorial is embedded below:
Download Redsn0w 0.9.6b5 for Windows
Download Redsn0w 0.9.6b5 for Mac

iPhone 4
iPhone 3GS
iPhone 3G
iPad
iPod touch 2G
iPod touch 3G
iPod touch 4G
Download iTunes 10.1 for Windows and Mac