Here is a step by step on how to Jailbreak iPhone 4, iPhone 3GS and iPhone 3GS running iOS 4.2.1 using RedSn0w 0.9.6b4 on a Mac. Follow all the instructions below to Jailbreak your device.
Note: Do not use this tool if you have to unlock your device, iOS 4.2.1 is not unlockable yet so you would have to wait for the release of updated Pwnage Tool.
Note 2: iOS 4.2.1 for iPhone 3G and iPhone 3GS is now unlockable. You can Jailbreak your device following this guide and then unlock your device using this guide (Link).
For iPhone 4 and iPhone3GS with newer bootrom the jailbreak is going to be tethered
For iPhone 3GS with older bootrom and iPhone 3G this jailbreak is untethered.
Things we need
RedSn0w 0.9.6b4
iOS 4.2.1 Firmwares. Select your phone below
- iPhone 4
- iPhone 3GS
- iPhone 3G
Instructions
1 ) Create a folder on your desktop Download RedSn0w and iOS 4.2.1 (links above) and place the files in ‘Pwnage’ folder you just created called Pwnage
2) Download RedSn0w (extract it) and iOS 4.2.1 (links above) and place the files in ‘Pwnage’ folder you just created
3 ) Connect your iPhone to the computer and launch iTunes and select your iPhone from the list of devices, now hold Options button and click on the Restore button.
4 ) Navigate to the Pwnage folder on your desktop and select the 4.2.1 firmware ipsw. Click the Choose button to continue.
5 ) Once iTunes has finished updating your iPhone to the desired firmware open the Pwnage folder on your desktop and launch the redsn0w application from the redsn0w folder we extracted earlier.
6 ) Once RedSn0w opens click the Browse button
7 ) Select the 4.2.1 firmware ipsw we placed in the Pwnage folder on our desktop then click Open. Once the firmware gets verified click the Next button to continue.
8 ) Let RedSn0w to prepare Jailbreak data.
9 ) From this window you can select the jailbreak options you would like make sure Cydia is selected.
10 ) Click the Next button to continue
11 ) Plug iPhone into the computer and make sure its OFF then click the Next button.
12 ) RedSn0w will now guide you through the steps to get into DFU mode. Follow the instructions displayed on your Screen.
Hold down both the Home button and the Power button for 10 seconds.
Release the Power button and continue holding the Home button until RedSn0w detects the device.
Keep the Home button pressed and release the power button, continue in this position for 15 seconds
13 ) Your iPhone should now reboot
14 ) RedSn0w will then begin uploading the new RAM Disk and Kernel.
15 ) Once uploading is complete you will be notified that RedSn0w is done. Click the Finishbutton. When your iPhone finishes rebooting (might take 5 minutes or more) it will be jailbroken with Cydia on the SpringBoard.
16 ) Done!
*To use Redsn0w to boot back into your jailbroken device simply select Just boot tethered right now from the options window and click Next. (iPhone 4 and newer iPhone 3GS users only)
Note 2: iOS 4.2.1 for iPhone 3G and iPhone 3GS is now unlockable. You can Jailbreak your device following this guide and then unlock your device using this guide (Link).
**Update: Chronic Dev Team has released its GreenPoison tool to untether jailbreak iOS 4.2.1 on iPhone, if you are running tether jailbreaked iOS 4.2.1 then you can simply untether it using this guide (link), its totally safe and will not delete your existing data on your device.
For any help regarding the jailbreak process please leave a comment below, we are here to assist you.