How to Unlock iPhone 3G(S) on iOS 4.2.1 with Ultrasn0w and Redsn0w [Guide]

As promised in our previous post, here is the step by step guide to unlock iOS 4.2.1 on iPhone 3G, 3GS using Reds0w and Ultrasn0w.

First we will update the baseband to iPad 06.15 and jailbreak the iPhone with Redsn0w. After the device is jailbroken, we can use Ultrasn0w from Cydia to unlock the device. Find the complete guide after the break.

Please read these instructions and warnings before you start the actual process:

  1. There is no way to come back down from 06.15, and there’s no hiding the baseband version from Apple.  You’ll be voiding your warranty in a very obvious way.
  2. If some future baseband comes out with a critical fix, you won’t be able to update to it if it remains down in the 05.xx sequence (then again, you wouldn’t update to it if you wanted to keep your unlock anyway).
  3. Starting with FW 4.2.1 if you have 06.15 on your iPhone you won’t ever be able to restore to stock firmware (it will fail).  You’ll need to only restore to custom IPSWs (then again, if you’re unlocker you should already be doing that).

Step 1: Download iOS 4.2.1 for your idevice.

Step 2: Download iTunes 10.1 and install it on your PC.

Step 3: Back up all the contents on your phone before you start the actual jailbreak process.

Step 4: Save the SHSH blobs if you are still on iOS 4.1 or below version. !very important

Step 5: Update/restore your device to iOS 4.2.1 via iTunes.

Step 6: Download Redsnow 0.9.6 beta 4 and run it.

Step 7. When asked for iOS firmware, point the redsn0w to iOS 4.2.1 downloaded in first step.

When you receive a pop-up message, click on Yes to confirm the baseband change.

Step 8: Click on next and select “Install Cydia” and “Install iPad Baseband” options. Optionally you can also select any other option available for your idevice.

Step 9: At this step make sure that your phone is switched off and plugged into the computer. Follow the onscreen instructions to put the idevice into DFU mode.

Step 10: Let Redsn0w do its work. Once completed your phone will restart and you will find it jailbroken on iOS 4.2.1.

Now if you have iPhone 3GS New bootrom you will have to connect it with Resnow and select the “Just boot tethered right now” option to get the jailbreaked state on every boot.

Jailbreak iOS 4.2.1 on iPhone 4, 3G, 3GS, iPad and iPod Touch using Redsn0w 0.9.6b4 RedSn0w Boot Tether


  • Download iOS 4.2.1 for your idevice
  • Download iTunes 10.1 for Win and Mac OS X
  • Download Redsn0w 0.9.6 beta 5 for Win and Mac

Note: Windows 7 or Vista users often need to use XP or 98 compatibility modes when launching redsn0w (right-click).

How to Unlock with Ultrasn0w 2.1:

After your device is jailbroken using the above mentioned procedure, open the Cydia App and search for Ultrasn0w. Install it and reboot your device. Your device is now unlocked.

Disclaimer: This guide is for educational and testing purpose only. This site will not be responsible for any type of damage. Use it at your own risk.

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By A. Usman

Loves new tech, especially from Apple and Google.

View all of A. Usman's posts.

22 Replies

  1. Smoothsays:

    iOS 4.2.1 3G and bb5.15.04 and ultrasn0w 1.2.5 does not unlock. Keep searching for signal. Any help ?!? Appreciate.

    1. You’ll have to update the baseband to iPad baseband using the Sn0wbreeze and then install the Ultrasn0w from Cydia.

  2. samadsays:

    i don’t want to change it to ipad baseband,is there any way else i can unlock it?

    1. Sorry no other way if you are on latest baseband.

  3. Gabrielle_p08says:

    why is this taking forever

  4. Greatguysays:

    Fuckin’ great, Works like a charm

  5. Vivienong49says:

    i have iphone 3g 4.2 05.15.04. i jailbroke my iphone by using Redsn0w 0.9.6 beta 5 and the 4.2 IPSW. i’ve also downloaded ultrasn0w on cydia. however, when i inset my tmobile sim card… nothing happens. only a one bar reception signal.

    how can i resolve this?

    thank u much

  6. Masouddehdarsays:

    it didnot worked for me.
    it keep searching then shows (no signal bars)

  7. Pjizzilsays:

    it worked for me. Only thing I had to do differently is install winterboard manually

  8. Jajalapidsays:

    how long does this take. I think I’m stuck on fetching basebands….

    1. Usually 5-20 minutes depending on the internet speed and load on Apple servers.

  9. Techkersays:

    will this work on APPLE TV 2G?

    1. Use pwnagetool, but it will be tethered jailbreak.

      1. Jayesh892says:

        it did work but now show no service or keep searching so can u give me the solution so that i can use it

  10. Mandasays:

    it does not work

  11. Mandasays:

    it does not work. tried it many times

  12. Challou47says:

    not doing thes its a stuped theng that you dan in your life you cant update you cant go back so you are in ipad not iphone its a stuped unlock

  13. Dansloansays:

    I’m very new to this but wanted to post. I upgraded to 4.2.1 and got new bb 5.15.04. I did as you said and upgraded to new bb 6.15.00 via redsnow. However I don’t like the tether unlock. So I went into itunes (with phone in recovery mode) and held the left shift key and clicked restore. I selected 4.1 firmware from previous download and restored 4.1. The phone was locked but i used tinyumbrella to kick myself out of recovery mode. Once out, i synced with itunes and was on 4.1 with 6.15.0 BB. I was then able to use Limera1n to jailbreak my phone (untethered), then installed utrasn0w 1.2. Now everything is working with my simple mobile simm.

    1. Choonhooisays:

      hi thanks for the info. It will be great if you could provide more details (step by step if you could) to jailbreak and unlock your phone.

      Here is the situation. My cousin got me a jailbroken and unlocked 3GS
      from UK. Put in my local SIM card, no problem. Everything works great.
      Then i itchy-hand, connect the phone to iTunes and clicked YES to update
      the phone to 4.2 (originally was 3.0). When everything done and
      rebooted the phone, my 3GS was locked out. iTunes says the SIM card is
      not supported, and on the screen of the phone, it just shows a USB cable
      plug to iTUnes. Is that what you were seeing too?

      I tried to various jailbreak methods found in
      the web (e.g redsnow, snowbreeze), to jailbreak and unlock it, but none
      of them works.

      Really appreciate your help.


  14. Anonymoussays:

    Awesome tutorial. Will use this asap.

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