I know its old but many of my users are asking about the Jailbreak tutorial of iOS 4.2.1 final version. I have collected all the links working that can help you jailbreak your Apple device running iOS 4.2.1. The main thing about it was the Redsn0w 0.9.6b4 as it was the first tool that bring proper Jailbreak for iPhone , iPod and iPad.
How To Jailbreak iOS 4.2.1 Final Version Using RedsnOw 0.9.6b4:
- Download iOS 4.2.1. Please download the firmware according to your respective device.
- Restore your device to iOS 4.2.1 using iTunes before continuing.
- Download Redsn0w 0.9.6b4.
- Now run it and browse for the iOS 4.2.1 ipsw.
- Now click next to start the Jailbreak process.
- Select check Cyida and press next to proceed.
- Now you’ve to follow the given instruction on the page to put your device in DFU Mode.
- After getting in DFU mode, RedsnOw will start the Jailbreak Process wait for it to be completed.
- When your device will be rebooted. iOS 4.2.1 Final Version Jailbroken Using Redsn0w 0.9.6b4.
- You can find more Jailbreak Tutorials here and also iPhone How To on iOS 7.
