iH8sn0w had released Sn0wbreeze 2.5.1 few weeks back, which allows users who want to jailbreak and also unlock their iPhone to update their iPhone with a pre-jailbroken iOS 4.3.1 while preserving the baseband from getting upgraded so that it can be unlocked using Ultrasn0w.

This guide will provide iPhone 4 and iPhone 3GS users with step-by-step instructions to update and jailbreak their iPhone with iOS 4.3.1 while preserving their iPhone’s baseband.

Some important points before the step-by-step instructions:

• Please note that jailbreaking your iPhone may void its warranty so proceed with caution.
• Don’t forget to backup your iPhone before you proceed. You can refer to this post for instructions on how to backup your iPhone.
• Please ensure that your iPhone has enough charge.
• This guide is only for iPhone 4 and iPhone 3GS users.
• iPad, iPod Touch and iPhone users who don’t care about unlocking or preserve their iPhone’s baseband can use Redsn0w to jailbreak their iOS device on iOS 4.3.1 as it is a lot easier.
• Sn0wbreeze is only works on Windows. Mac OS X users should use PwnageTool. Checkout this step-by-step guide.
• Users who want to unlock their iPhone:
  • Sn0wbreeze does not unlock your iPhone.
  • You can use Ultrasn0w to unlock your iPhone after you have successfully updated and jailbroken your iPhone  with iOS 4.3.1.
  • But there is a catch. Ultrasn0w 1.2.1 can only unlock the following basebands (you can check the baseband by going to Settings –> General –> About –> Modem Firmware):
    • iPhone 4 baseband – 01.59.00
    • iPhone 3GS basebands – 04.26.08, 05.11.07, 05.12.01, 05.13.04 and 06.15.00.
  • So if your iPhone is currently on baseband mentioned above then Sn0wbreeze will allow you to create a custom pre-jailbroken iOS 4.3.1 and preserve the baseband so that you can unlock your iPhone using Ultrasn0w 1.2.1.
  • If you accidentally upgraded your iPhone 4 with iOS 4.3.1/iOS 4.3/ iOS 4.2.1/ iOS 4.1 then its baseband would have got upgraded to 02.10.04/ 03.10.01/ 04.10.01. Unfortunately, 02.10.04, 03.10.01, 04.10.01 basebands for iPhone 4 cannot be unlocked nor can it be downgraded currently.
  • Similarly, if you accidentally upgraded your iPhone 3GS with iOS 4.3.1/iOS 4.3/ iOS 4.2.1/ iOS 4.1 then its baseband would have got upgraded to 05.14.02/ 05.15.04/ 05.16.01/ 05.16.02. Unfortunately, 05.14.02, 05.15.04, 05.16.01, 05.16.02 basebands for iPhone 3GS cannot be unlocked nor can it be downgraded currently.
• After the jailbreaking process is complete, do not forget to checkout our article on tips to keep your iPhone secure. Also, remember to change the password of your jailbroken iPhone.
• Please read the instructions carefully especially the ones highlighted in bold.

If you meet the requirements mentioned above then you can proceed with the step-by-step instructions to jailbreak your iPhone using Sn0wbreeze.

Step 1: Download Sn0wbreeze 2.5.1 from here and save it in a folder named “Sn0wbreeze” on your desktop.

Step 2: You also need to download the iOS 4.3.1 firmware file (use Firefox or Chrome to download the firmware file instead of using Internet Explorer or Safari):

iOS 4.3.1 firmware file for iPhone 4 users (iPhone3,1_4.3.1_8G4_Restore.ipsw)

iOS 4.3.1 firmware file for iPhone 3GS users (iPhone2,1_4.3.1_8G4_Restore.ipsw)

Step 3: Extract Sn0wbreeze from the zip file. Double click on the Sn0wbreeze icon to launch the application. You will get a dialogue informing you that the software is not for commercial use. Click OK button to continue. Then the Credits dialog box, click on the Close Credits button to continue.

Step 4: Click on the blue arrow button at the bottom right side to proceed.

Step 5: Click on the browse button and select the appropriate firmware file that you had downloaded in step 2 (iPhone 4 users: iPhone3,1_4.3.1_8G4_Restore.ipsw, iPhone 3GS users: iPhone2,1_4.3.1_8G4_Restore.ipsw) .

Step 6: Sn0wbreeze will verify the firmware file. Once the firmware file is verified, it will you inform you that the IPSW is verified and also the iPhone model. You will be able to click on the blue button to proceed. For iPhone 3GS users, it will request you to select whether your iPhone 3GS comes with the old or new bootrom. If you don’t know, click on the Detect it for me button. You need to connect your iPhone and follow the on-screen instructions.

Step 7: After selecting the bootrom, you will be prompted with three options:

• Baseband Preservation Mode
• Simple Mode
• Expert Mode

Select Expert Mode and then click on the blue arrow. Note all modes preserve the baseband so you can also select the Simple Mode. Baseband Preservation Mode will only update your iPhone to iOS 4.3.1 while preserving the baseband but won’t jailbreak your iPhone.

Step 12: Sn0wbreeze will now start creating the custom firmware file, which takes 5 to 6 minutes. You will get an option to play PacMan during this time.

Step 13: Once the custom firmware file is create, you will get a message that the custom firmware has been successfully creation and prompted with an OK button to put your device in a restorable state. Sn0wbreeze creates the custom firmware file on your desktop and prefix it with sn0wbreeze. So it will create sn0wbreeze_iPhone 4-4.3.1.ipsw for iPhone 4 users and sn0wbreeze_iPhone 3GS-4.3.1.ipsw file for iPhone 3GS users.

Step 14: Turn off your iPhone and connect it to the computer and follow the on-screen instructions to put your iPhone in DFU mode using Sn0wbreeze:

• Hold Power and Home buttons for 10 seconds
• Now release the Power button but continue holding the Home button for 10 more seconds
• You device should now be in DFU mode

Step 15: If you’ve followed the steps correctly, you should get a message that your device is in a PWNED DFU state (black screen).

Step 16: iTunes will now prompt you with a message that reads “iTunes has detected an iPhone in recovery mode“. Press OK. Your iPhone is now in recovery mode.

Step 17: While on the iTunes window, hold the Alt/Option SHIFT key and click on the ‘Restore‘ button. (This is a VERY IMPORTANT STEP as just pressing the “Restore” button will result in restoring your iPhone with the latest firmware, which is iOS 4.3.1 firmware currently, by holding down Alt/Option button, allows you choose the custom iPhone firmware file).

Step 18: Navigate to the Pwnage folder on your desktop and select the custom IPSW file (REMEMBER the custom firmware file with sn0wbreeze prefix) that was just built (and NOT the original firmware file). Click on the ‘Choose‘ button to proceed.

Step 19: iTunes will now restore the custom firmware on your iPhone. The process will take up to 10 minutes. Once it is completed, your iPhone will reboot and should be updated with iOS 4.3.1. It should also be successfully jailbroken and you should find Cydia jailbreak app on your iPhone’s home screen.

If you’re new to the jailbreaking world and wondering what to do after jailbreaking your iPhone, checkout our jailbreak apps category page to find out the apps you can install on your iPhone using the Cydia app.

Update:

Updated the post to use the Expert Mode.

If you observe the single signal bar issue after successfully jailbreaking your iPhone, install Ultrasn0w 1.2.1 by following the step-by-step instructions mentioned here.

We hope you found this tutorial useful. Please let us know how it goes in the comments below.