Upgrading your iPhone to the latest iOS 4.2.1 can be a nightmare to some of you who love to jailbreak or unlock. Upgrading to the latest iOS simply means getting, of course, a new iOS with new enhancements and also a newer version of baseband. Problem is, even if you have successfully downgraded your iOS, your baseband won’t follow suit.
Now you know how important to preserve the baseband so that your iPhone remain unlockable. So here’s the step-by-step guide on how to update iPhone 4 to iOS 4.2.1 while preserving baseband 02.10.04 and 01.59.00. Be sure to have your SHSH blobs saved for iOS 4.1 & 4.2.1 before updating.
What you need for this update process?
How to update iPhone 4 to iOS 4.2.1 while preserving baseband?
1. Browse through the following directory path C:\Windows\System32\drivers\etc\ and find a file named “hosts“. Right click on the file and select “Run as administrator“. Add the following ip address like in the screenshot below and save it.
2. Connect your iPhone 4 to PC via usb cable. If iTunes doesn’t start automatically, open it manually.
3. Keep holding Shift button on Windows @ Option on Mac and click on the update button on iTunes. Browse through the folder where iOS 4.2.1 firmware file resides.
4. Now let the update process to continue. When you almost finish, there will be an error popup from iTunes. It should be there, so there is nothing to be worried about.
5. Start TinyUmbrella. From the left pane, select iPhone 4 from “Recovery Devices“.
6. Click on “exit recovery” button.
7. iPhone 4 should reboot itself and you are done!
8. You can check whether everything goes as planned by checking your iOS and baseband version. The status should read iOS 4.2.1 with baseband 02.10.04 (or 01.59.00).