Jailbreak IOS 4.2.1 on Iphone 3G FU using Redsn0w

A couple days ago, DevTeam released their newest jailbreaking tool (Redsn0w 0.9.6b4 with compatibility of cydia and mobile substrate with IOS 4.2.1) that can used to jailbreaking IOS 4.2.1.

First of all, i would like to say big thanks to devteam that make this jailbreak happen… you guys are awesome 😀

Please backup your data in your iphone before doing this jailbreak.

note #1 : If you are an unlockers or Iphone Software Unlock users, you should check Dev Team blog in here to make sure your iphone is jailbreakable (cause it will updated your iphone baseband to 05.15.04. If you accidentally updated your baseband, you need to wait for devteam to release new ultrasn0w to do unlock).

note #2 : after i jailbreak my iphone to ios 4.2.1 using this redsnow, i found some problems.  When i switched running application from multitask bar, it always crash and respring.

note #3 : Qtweeter 3.6.4 doesn’t want to run in this IOS 4.2.1. Got no luck for this one.. 😦

What you need?

  1. IOS 4.2.1 stock firmware, u can grab from here.
  2. itunes 10.1, u can grab from here.
  3. Redsn0w 0.9.6b4, u can grab from here.
  4. Your Iphone 3G FU (Factory Unlock).

Jailbreaking Step

  1. Plug in your iphone to your PC, and run Itunes 10.1.
  2. Restore your iphone using IOS 4.2.1 stock firmware by hold shift key in keyboard and click restore button. It will show up a dialog to locate your IOS 4.2.1 stock firmware. Wait until restoring progress complete.
  3. Locate your downloaded redsn0w, and extract it.


  4. Run redsn0w application from folder you extracted earlier. If you are in windows 7, please run redsnow using xp compatibility mode and run as administrator.


  5. Click on browse button, and locate IOS 4.2.1 stock firmware. Press next and redsn0w will verify selected firmware. Press next when verified has been completed.


  6. Select the IOS 4.2.1 stock firmware that you have downloaded, and press ok to continue.


  7. Redsn0w will verified your selected IOS firmware.


  8. Once it’s finished, press next to continue. Redsn0w will began preparing jailbreaking data.


  9. In redsn0w jailbreak option section, make sure you select install cydia option to enable cydia in your iphone, enable multitasking option (optional) to enable multitask feature in your iphone and enable battery percentage option (optional). You could also enable homescreen wallpaper option if you like, but I recommend that you not select this option, while it’ll be make your iphone run very slow. After you setup all of option, press next to continue.


  10. Make sure your iphone plugged in to your PC and turn your iphone off, and press next to continue.


  11. Follow redn0w instruction to enter DFU mode. If you failed entering DFU mode for your iphone, jailbreak process won’t continue.




  12. Redsn0w will begin jailbreaking process automatically, once you have entered DFU mode successfully. Wait for jailbreaking process until it’s finished (on redsn0w and your iphone). Once all jailbreaking process is finished, you will see cydia on the springboard.
  13. That’s it, now you have a jailbroken iphone 3G running on IOS 4.2.1
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