How to Jailbreak and Unlock iOS 4.2.1 on iPhone 4 using Greenpois0n [Mac]

How to Jailbreak and Unlock iOS 4.2.1 on iPhone 4 using Greenpois0n [Mac]

This guide will help you perform an iOS 4.2.1 untethered jailbreak on your iPhone 4 and also unlock it if required. We will be using Greenpois0n’s latest release to jailbreak iPhone 4 using a Mac computer. Please note that Unlock is only available to iPhone 4’s at baseband version 1.59.00

What Files do you need?

  1. Greenpois0n – Link
  2. iOS 4.2.1 firmware file for iPhone 4 – Link

iOS 4.2.1 Jailbreak Procedure:

If you do not have a factory unlocked iPhone 4 and rely on software based unlock like Ultrasn0w you should be careful not to update baseband version else you will lose unlock forever. Read how to Upgrade iPhone 4 to 4.2.1 safely preserving baseband before proceeding.

Extract Greenpois0n from the archive you downloaded above and run the file.


Turn off your iPhone 4 after connecting it to your computer and press the Jailbreak button. You should now see instructions to put iPhone into DFU mode. Follow them as shown on the screen.




If you fail to do it right you will be prompted to try again. Don’t worry and give it another try patiently. In case you get it right Greenpois0n will start jailbreaking your iPhone 4.

Once the Jailbreak is over click on the complete button and wait for your iPhone to restart.


You should now be able to see a new application called Loader on your iPhone screen.

Iphone greenpois0n loader

Tap on Loader and then select Cydia. Tap on install Cydia.

Iphone greenpois0n loader 2

Once Cydia has installed tap on Remove Loader. That’s it your iPhone 4 is now jailbroken with Cydia installed. If you need to unlock your iPhone 4 read How to Unlock iOS 4.2.1 on iPhone 4 with Ultrasn0w.

If you have any questions or got stuck in any step feel free to ask us via comments.

Article by Rajat

Rajat has written 225 articles.

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{ 8 comments… add one }

  • Sandip February 5, 2011, 8:28 am

    Seriously you should get the facts clear before writing any thing like this which will be risking iPhone 4 users, iOS 4.2.1 Baseband 3.10.01 can’t be unlocked.

  • Rajat February 5, 2011, 8:49 am

    what part of the tutorial said that the firmware you mention can be unlocked?
    there’s a clear warning mentioned for iPhone 4 users relying on software unlocks. noway anyone can overlook that.

  • Sandip February 5, 2011, 4:07 pm

    Post title “How to Jailbreak and Unlock iOS 4.2.1 on iPhone 4 using Greenpois0n [Mac]” does it says any where unlock is on baseband 1.59.00 isn’t you title misleading ??

  • Rajat February 5, 2011, 8:07 pm

    first things first Sandip, what part of the tutorial risked any iPhone 4 users?

  • bethers98

    February 6, 2011, 3:07 am

    Very confusing and even more irritating…. I have yet to unlock my iPhone 4.2.1 version 3.10.01 and after reading the above post AFTER attempting to download/install the latest Greenpoison untethered JB I’m beginning to question your site. I was looking for help when I had trouble with the instructions (telling me to press the “home” and “sleep” button on a Mac). There are no such buttons on my Mac keyboard, and the instructions were supposed to be written for a Mac. What gives???

  • Rajat February 6, 2011, 6:00 am

    if you had read the post before attempting to install or downlaod anything, you might have saved yourself a lot of effort.
    while i have all my sympathy for you its the first time i came across someone who can’t locate home/sleep buttons but can understand what the terms untethered, jailbreak and unlock mean.

  • Hoss

    February 15, 2011, 7:36 am

    hi Rajat,

    need you help please. got i phone 4 with firmware 4.2.1 and baseband 3.10
    i jailbreak it ,but i need to unlock it, can you help.

    also is it possible to downgrade to another baseband ,to unlock it ,and how???

    i just bought from usa locked on AT&T and want to use it on another carrier


    March 2, 2011, 2:55 pm

    I used this progrm.. had to jailbreak and unlock as i moved from Canada to Mexico. Works awesome! it would not turn back on for about 3 hours. I restarted the origional process and it worked like a charm

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