How to Update iPhone 4 to iOS 4.2.1 While Preserving Old 01.59.00 Baseband for Unlock

If you have an iPhone 4 with the older and unlockable 01.59.00 baseband, and you want to upgrade to the latest iOS 4.2.1 while preserving your baseband, i have a solution for you. The following method will allow you to upgrade your iPhone 4 to iOS 4.2.1, while preserving the 01.59.00 baseband which is unlockable using Utrasn0w 1.2
This method is known to work only with the iPhone 4, hence it may not work on other devices. The procedure seems fairly simple! We highly recommend you to backup everything on your device before following the procedure
Step 1: Download the CUSTOM l iOS 4.2.1 firmware for iPhone 4 from here.
MEGAUPLOAD - The leading online storage and file delivery service
Step 2: Now trick iTunes into thinking that it is watching Apple servers, while in real, we are going to change the address to Saurik’s server. To do this:
Navigate to C:\Windows\System32\drivers\etc\ and locate “hosts” file.

Open this “hosts” file in Notepad (for Windows) or TextEdit (for Mac OS X) and add this
74.208.105.171 gs.apple.com

Now simply save this file and you are good to go!

NOTE for Windows 7 and Vista: Start “Notepad” with Administrator privileges by right clicking on “Notepad” app, and click on “Run as Administrator“ option.

NOTE for Mac OS X: Make sure you have full read and write access on your account when you are saving the host file. If it still throws permission error, simply copy the host file to desktop, make the required changes, and then replace it with the original file in “/etc/” directory.
STEP 3;open redsnow browse 4.2.1 stock firmwaer(everything u know how to go in dfu mood)
Step 4: Start iTunes, click on your iOS device icon from the sidebar in iTunes. Now press and hold left “alt” (option) button on Mac, or Left “Shift” button if you are on Windows on the keyboard and then click on “Restore” (Not “Update” or “Check for Update”) button in the iTunes and then release this button.


This will make iTunes prompt you to select the location for your iOS 4.2.1 CUSTOM file. Select this custom f file and click on “Open” to restore your iPhone. successfully installed on the device without the upgraded baseband.

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Once you have completed this procedure, Go to Settings –> About on your iPhone, and scroll down to check your Model Firmware (Baseband), which should now read 01.59.00 (which of course is unlockable using Ultrasn0w). You should now be able to jailbreak your iPhone 4 on iOS 4.2.1 (tethered) using Redsn0w 0.9.6, or untethered using Redsn0w 0.9.7. Once you have jailbroken your iPhone 4, you can safely unlock it on iOS 4.2.1 (on 01.59.00 baseband) using Ultrasn0w 1.2.

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