How to Update iPhone 4 to iOS 4.2.1 [Old 01.59.00 Baseband Preserved] for Unlock

If you want to kill two birds with one stone by upgrading your iPhone 4 to latest iOS 4.2.1 with preservation of your older & unlockable 01.59.00 baseband, here is the complete tutorial for this purpose. This step-to-step tutorial will guide you to upgrade your cute iPhone 4 to iOS 4.2.1 without damaging its previous 01.59.00 baseband to go further for unlocking it with Ultrasn0w 1.2.

Only iPhone 4 users can follow the tutorial described here as it is specifically designed for iPhone 4. The tutorial makes the upgrading process very easy to follow, but to avoid from any discrepancy you should have a back up of all necessary files before adopting the steps given here for your convenience. And finally do the all at your own risk as usual.

Here is the step-to-step tutorial for upgrading your iPhone 4 to iOS 4.2.1, while preserving your old 01.59.00 baseband (unlockable) at the same time.

Step -1:

First of all, download the original iOS 4.2.1 firmware for iPhone 4 from here.

Step -2:

Then ploy iTunes into supposing that it is watching Apple servers, however actually, we will change the address to Saurik’s server. How? Here is the way;

Browse for C:/Windows/System32/drivers/etc/ and locate “hosts” file.

Mac OS X users can also get to “/etc/” directory by “Go –> Go to Folder” from Finder.

• Open “hosts” file in Notepad (for Windows) or TextEdit (for Mac OS X) and insert this line;

74.208.105.171 gs.apple.com

If you have done it successfully, half done is well done too!

Note Please!

• For Users of Windows 7 & Windows Vista: Start “Notepad” with Administrator rights by right clicking on “Notepad” app, and then click on “Run as Administrator“.
• For users of Mac OS X: Ensure that you have a full read and write access on your account while saving the host file. If permission error occurs, copy the host file to desktop, do the required changes, and then change it with the original file in “/etc/” directory.

Step -3:

Open iTunes, click on the icon of your iPhone 4 tablet from the sidebar in iTunes. Then Press and Hold left “alt” button [For Mac Users] OR left “Shift” button [for Windows users] on the keyboard, now click on “Restore” button in the iTunes and release the button softly.

iTunes will surely prompt in front of you to select the location of your iOS 4.2.1 firmware file. Find this IPSW file and then click on “Open” to restore your iPhone.

Step -4:

During restoring to iOS 4.2.1, iTunes will prompt 1013 error. Don’t worry; just ignore it since the firmware has already been installed on your iPhone 4 without the upgraded baseband.

Step-5:

Here, your device will stuck in Recovery Mode, displaying “Connect to iTunes” screen.

Now download Tinyumbrella jailbreak tool (Windows / Mac) to exit your iPhone 4 from Recovery Mode. Run Tinyumbrella software, and then click on “Exit Recovery” button. If your device restarts, it’s OK.

Now you have upgraded your iPhone 4 to iOS 4.2.1 while preserving your old 01.59.00 baseband rightly. It enables you to jailbreak your iPhone 4 on iOS 4.2.1 (tethered) using Redsn0w 0.9.6, or (untethered) using Redsn0w 0.9.7.

If you have jailbroken your iPhone 4, you are quite able to unlock it on iOS 4.2.1 (on 01.59.00 baseband) using Ultrasn0w 1.2 without any fear.

[Thanks to Ven000m for this handy method]

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