Let me clear this upfront. This is strictly for iPhone 3G and iPod touch 2G (non-MC model) only.
If your iPhone 3G relies on an unlock, DO NOT update to iOS 4.1 Beta now as the current version of ultrasn0w cannot unlock this new firmware.
If you have iPhone 3G (which doesn’t rely on an unlock), or an iPod touch 2G (non-MC model), then simply follow the guide posted to below jailbreak your device on iOS 4.1 Beta using Redsn0w 0.9.5b5-5.
Step 1: Download iOS 4.1 Beta for your version of iPhone and iPod touch. Download link here.
Step 2: Update to this latest firmware using the IPSW file you just downloaded (download links here).
Step 3: Start Redsn0w 0.9.5b5-5 (download link given below) and point it to iOS 4 (Final Version), and not iOS 4.1 firmware file to proceed.
Step 4: Now select “Install Cydia” and click “Next”.
Step 5: Now make sure your device is both OFF and PLUGGED IN to the computer before you click “Next”.
Step 6: Connect your device in recovery mode by pressing the Power and buttons continuously.
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 7: Sit back and enjoy while redsn0w will do all the rest for you. Once done, your iPhone and/or iPod touch will restart automatically and you will find it jailbroken on the latest iOS 4.1 Beta firmware.
Disclaimer: This guide is for testing & educational purposes only. I’m not responsible for any loss of important data or malfunctioning of your iPhone.