GreenPois0n RC5 jailbreaks iphone 4 iOS 4.2.1 untethered (and other iOS devices too).
Unlike Redsn0w 0.9.7, Greenpois0n don’t require you to have SHSH blob of 4.2b3 saved on Cydia. You can jailbreak your iPhone 4 on iOS 4.2.1 using GreenPois0n.
These instructions are to jailbreak iOS 4.2.1 on iPhone 4, iPhone 3Gs, iPod touch 2G/3G/4G, iPad and Apple TV 2G using greenpoison.
Notes:
Don’t upgrade your iPhone directly from iTunes.
If you’re on Redsn0w tethered jailbreak already, you can run GreenPois0n over it to make your iPhone 4 untethered Jailbreak
Required Downloads:
UPDATE 4: Windows version of GreenPois0n is now available for download. More details here.
Download (link not working: http://www.greenpois0n.com/ ) GreenPois0n [Mac OS X Mirror (link not working: http://mirrors.ih8sn0w.com/greenpois0n-osx_rc5_2.zip ) ]
Download (link not working: http://www.greenpois0n.com/ ) GreenPois0n for Windows [Mirror (link not working: http://mirrors.ih8sn0w.com/gp_win_rc5_b2.zip ) ]
Download iOS 4.2.1 for iPhone 4, 3GS, iPod touch 4G / 3G / 2G and iPad
How to Jailbreak iPhone 4 iOS 4.2.1
1. Download GreenPois0n and run it.
2. Connect iPhone 4 to your computer using usb and click “Jailbreak” on GreenPois0n screen.
3. On next page follow onscreen instructions to enter DFU mode.
4. Once your iPhone 4 is in DFU mode, jailbreak procedure will start automatically
5. Once the jailbreak is complete, goto your iPhone 4 homescreen and click loader app and install Cydia.
6. You’re now done, your iPhone 4 jailbreak on iOS 4.2.1 is complete. Now you can install apps using Cydia.