We have already shared how to jailbreak and unlock iOS 4.2.1 on Mac using greenpois0n and here is quick tutorial on how to Jailbreak unlocked iPhone running iOS 4.2.1.
Greenpoison rc5 beta 4 will let you get an untethered jailbreak. You can download the latest version of GreenpoisOn here.
Step by step guide to Jailbreak iOS 4.2.1
- Download and open GreenpoisOn
- Switch off your iPhone and connect to your computer
Click on prepare to Jailbreak and get into DFU mode by following onscreen instruction. Once you followed the instruction carefully to get into DFU mode, your phone will get into DFU mode and click on jailbreak.
Now sync your iPhone and enjoy jailbroken app on Jailbroken iOS 4.2.1. Do let us know if you have any question regarding jailbreaking our iPhone.