Dev-Team has release RedSn0w 0.9.6b4 to jailbreak iOS 4.2.1 on iPhone 4, 3GS, 3G, iPod touch 4G, 3G, 2G and iPad. RedSn0w 0.9.6b4 jailbreaks iOS 4.2.1 with working Cydia and MobileSubstrate. Step-by-step instructions on how to jailbreak iOS 4.2 with RedSn0w 0.9.6b4 after the jump…
RedSn0w 0.9.6b4 is capable of jailbreaking all iDevices on iOS 4.2.1 however, newer devices are tethered jailbreak only. A tethered jailbreak means that each time your device loses battery power or needs to be rebooted, you must attach it to a PC or Mac to boot into the jailbroken state.

Untethered Jailbreak: iPhone 3GS (old bootrom), iPhone 3G, iPod touch 2G (Non-MC)
Tethered Jailbreak: iPhone 4, iPhone 3GS (new bootrom), iPad, iPod touch 4G, iPod touch 3G, iPod touch 2G (MC Model)

WARNING: unlockers please stay far far away from this official firmware (and all official firmware). Wait for the ability to create custom 4.2.1. IPSWs that don’t update your baseband! If you’re not an unlocker, read on!

Lets jailbreak iOS 4.2.1 firmware on iPhone 4, 3GS, 3G, iPod Touch 4G, 3G, 2G and iPad with RedSn0w 0.9.6b4.

How to Jailbreak iOS 4.2.1 with RedSn0w 0.9.6b4

Step 1

• Download iOS 4.2.1
• Download RedSn0w 0.9.6b4 for Windows [Mirror 1] [Mirror 2]
• Download RedSn0w 0.9.6b4 for Mac [Mirror 1] [Mirror 2]
• Download iTunes 10.1

Step 2

Connect your iDevice to the iTunes 10.1 and restore iOS 4.2.1.
ATTENTION iPhone Users: iOS 4.2.1 will update your baseband which is not unlockable ATM.

Step 3

Once your iPhone / iPod Touch / iPad is running iOS 4.2.1, execute the downloaded RedSn0w 0.9.6b4.

Step 4

Hit the Browse button and select the downloaded iOS 4.2.1 firmware. RedSn0w will recognize the firmware, now hit the Next button.

Step 5

Now select your desired options. Make sure that atleast Install Cydia is selected. Now hit Next button.

Step 6

RedSn0w will ask you to turn off your device. When it’s off and plugged in, hit the next button.

Step 7

Now you’ll be instructed to put your device into DFU Mode. Follow the on screen instructions.

Once your device goes into DFU mode, RedSn0w will start jailbreaking it. Once done, you can find the Cydia icon on your iPhone / iPod Touch / iPad home screen.

That’s it. You’ve successfully jailbreak iOS 4.2.1 on iPhone 4, 3GS, 3G, iPod touch 4G, 3G, 2G and iPad with RedSn0w 0.9.6b4.

How to Boot Tethered jailbroken Device after reboot:

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