RedSn0w has been updated to version 0.9.6b5 which will jailbreak iOS 4.2.1 on iPhone 3GS, 3G and iPhone 4 and will update the baseband to 06.15 on iPhone 3GS and 3G so make it unlockable. iPhone 4 users are still out of luck and we will update you as soon as iPhone 4 unlock is release. Follow our guide below for both mac and windows on how to jailbreak iOS 4.2.1 on RedSn0w 0.9.6b5 and update baseband to 06.15 after the break. If you have an old-bootrom 3GS and are already unlockable but want to get to 4.2.1, please wait til iPhone Dev Team release an “unofficial” bundle for you.

For More Information On How To Unlock Your iPhone visit: www.bestunlockiphone.com

The new redsn0w 0.9.6beta5 is out. It gives both Windows 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 currently getting pounded).
Important Note: RedSn0w not only jailbreak your iOS 4.2.1 but it also updates the baseband 5.14.02 and 5.15 to 6.15 for iPhone 3GS and 3G so make it unlock. Now there are some key points which should be note before proceeding with this Jailbreak and unlock tool.
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.
Here is a Step by Step Guide on how to Jailbreak iOS 4.2.1, and update baseband of iPhone 3GS and 3G to 6.15.
Step1:
Download your respective iOS 4.2.1 firmware Here
Download RedSn0w 0.9.6B5 Here
Download RedSn0w 0.9.6B5
Step2: Update and restore your iPhone firmware to iOS 4.2.1 using iTunes 10.1. Open iTunes and select your iPhone in sidebar, Windows users press “shift” and restore and browse the firmware. Mac users press “Alt/Option” and Restore and browse to iOS 4.2.1 firmware.
Step3: Launch RedSn0w 0.9.6B5 and “browse” your iOS 4.2.1 Firmware.
Step4: Now there will be different options as shown below in picture, select “install Cydia” and “install iPad Baseband” So iPad Baseband 06.15 will be ported to iPhone 3GS and 3G and will make it ready for unlock. Don’t select custom boot logo and recovery logo if you don’t want to.

Step5: Now make sure your iDevice is connected to computer and turned off. Now click Next.
Step6: There will be some instructions on Redsn0w as shown below on how to put your device in DFU mode, follow it
Step7: when your Device entered in DFU mode so click next and your installation of custom firmware with baseband 06.15 will start.