How to Update iPhone 4 to iOS 4.2.1 Safely Without Upgrading Baseband

This tutorial will show you show how to update iPhone 4 to iOS 4.2.1 without upgrading your baseband. This method will preserve iPhone 4’s baseband at 1.59.00 so you don’t lose your software unlock using Ultrasn0w in case you don’t have a factory unlocked iPhone.

If you have a factory unlocked iPhone 4 you don’t need to worry about your baseband since your iPhone will always stay unlocked.

In case you don’t know what your existing firmware version or baseband version is please first read How to Find iPhone Firmware and Baseband Version. Proceed only if you are on iOS version less than 4.2.1 and Baseband version 1.59.00.

As of present day only the iPhone 4’s at baseband version 1.59.00 are unlockable using Ultrasn0w. If you have any other baseband version this tutorial will not work for you.

Tools Required to use this Guide:


Download these first:

  • iOS 4.2.1 Firmware for iPhone 4 – Download here
  • TinyUmbrella – Software to preserve baseband
  • Greenpois0n to jailbreak iPhone – Download link

Steps to Update iPhone 4 to iOS 4.2.1 Safely:

Connect iPhone 4 to your Mac and launch TinyUmbrella after you install it. Click on Save SHSH.


Click on Start TSS Server and then Launch iTunes

Click on Alt+Restore and point iTunes to the IPSW firmware file you downloaded previously.


iTunes will report Error 1013 after the restoration is over. Don’t panic. It means all is going as intended so far. Jailbreak iPhone 4 using Greenpois0n. The iPhone 4 should be out of Recovery after the jailbreak is done.

Activating iPhone:

The drawback of Greenpois0n is that unlike PwnageTool or other jailbreak tools, it does not support hacktivation. You will have to insert the official SIM card. For example, if phone was purchased in the US, you need to insert an AT&T sim card to activate it the first time. You don’t need official SIM after this.

Install Ultrasn0w from Cydia using this guide and enjoy iOS 4.2.1 on your iPhone 4.

Follow the steps exactly as stated above and your baseband will remain untouched. In case you don’t understand any step feel free to ask via comments.