Guide: How to use Redsnow to jailbreak iOS 4.2.1 on iPhone, iPad, and iPod Touch

In this post I'm going to present to you the method to jailbreak your iDevices (iPhone,iPad,iPod touch) running on iOS 4.2.1

Disclaimer: Please proceed with this Jailbreak at your own risk. I will not be responsible for any mishaps or device failure upon attempting this method.

Jailbreak type:  

• Tethered for iPhone 3GS (new bootrom), iPhone 4, iPad, iPod touch 2G (MC Model), iPod  touch 3G and the iPod touch 4G
• Untethered for iPhone 3GS (old bootrom), iPhone 3G and iPod touch 2G (Non-MC Model)

Warning: PLEASE STAY AWAY from this Jailbreak for those on who rely on carrier unlock. This Jailbreak WILL NOT unlock your iPhone.

Tools (Download): 

1. iOS 4.2.1 for iPhone 4, 3GS, 3G, iPad, iPod touch
2. Redsn0w 0.9.6b4 for Windows or for Mac
3. iTunes 10.1 for Windows or Mac

Steps:

1. Download the appropriate version of iOS 4.2.1 depending on your device.
2. Update or Restore your devices using the iOS 4.2.1 you've just downloaded earlier. (A prior backup of your apps and data are advisable upon restoring/updating to 4.2.1)
3. Launch Redsn0w 0.9.6b4 and load the previously downloaded iOS 4.2.1 and then select the 4.2.1 firmware and click 'Open'.
4. Click 'Next' and Redsn0w will begin injecting the firmware for Jailbreaking.
5. Check the 'Install Cydia' option and click 'Next'.
6. Turn your iDevice into DFU mode by shutting down your iDevice and plugging in your iDevice and click 'Next'.
7. Follow the sets of instructions on the screen to boot your iDevice into DFU mode. (Repeat if fail)
8. Wait until the process is complete and after your iDevice has restarted, it will be with the latest iOS 4.2.1 jailbroken firmware.

Additional Step for iPhone 4, 3GS (New Bootrom), iPod touch 4G / 3G / 2G, and iPad ONLY (Tethered)
    9.  Use Redsn0w and repeat step 3-5 but in this case for step 5 uncheck 'Install Cydia' and select 'Just boot tethered right now' after each REBOOT/RESTART of your system to put your iDevices in 'Jailbreak State'..