As stated the GreenPois0n is fully capable to jailbreak any iOS device. Our friends at RP have shared a few steps on how to jailbreak the iOS 4.2.1 on the iPhone 4, iPhone 3GS, iPod Touch, Apple TV and the iPad. Those steps are:
1. Download GreenPois0n and connect your iPhone or other iOS device to your computer. Once done simply hit jailbreak.
2. Enter the DFU mode by holding the Sleep button.
2a. Continue with holding the sleep button and press the Home button.
2b. Release the sleep button and continue holding home.
3. With the previous procedure completed, GreenPois0n will now jailbreak your iPhone untethered on the iOS 4.2.1.
4. Upon successful jailbreak, you can initiate Loader on the homescreen to install Cydia.
The initial release was a bit buggy so there has been an update with the GreenPois0n RC5_2. As for those who already have a tethered jailbreak using the Redsn0w 0.9.6 can simply run GreenPois0n to untether the existing jailbreak.
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