Every iPhone has separate baseband chip different from processor, used to communicate with antenna. A separate code is used to communicate with baseband chip while making or receiving calls & its baseband which decides whether you can unlock your iPhone or not.

If your iPhone 4 has iOS 4.0.1 with baseband 1.59.00 then you can unlock it using Ultrasn0w 1.0-1 but if you update to iOS 4.1 then your baseband will be updated to 2.10.4 for which no unlock tool is available yet. Now only two options are left,

1. Either don’t update to iOS 4.1 at all

2. Or preserve baseband by some means and update to iOS 4.1.

On same mechanism PwnageTool works, which let you to create custom firmware preserving baseband, unfortunately Pwnagetool for iPhone 4 is not yet available.

Well no need to disappoint, Notcom developer behind TinyUmbrella tool for saving SHSH blobs has come up with latest version of TinyUmbrella 4.1.3 which lets you to update iPhone 4 to iOS 4.1 WITHOUT updating your baseband. Yes that’s right, now you can update to iOS 4.1 preserving baseband thereby retaining unlockabled baseband.

Follow below step by step guide to update to iOS 4.1 without updating Baseband

How to Update iPhone 4 to iOS 4.1 Without Updating Baseband

1. Get the latest TinyUmbrella (4.1.3)

2. Make sure to READ THE README TinyUmbrella File

3. Run TinyUmbrella.

4. Start TSS Server

5. Open iTunes

6. Download iOS 4.1 and use iTunes Restore (NOT UPDATE) to update to iOS 4.1

7. Let iTunes error with 1004 error (baseband update failed – we want this :) )

8. Kick Device Out of Recovery

That’s it You are now on 4.1 with 1.59.00 baseband!

Even though you have preserved baseband you won’t be able to unlock since no jailbreak tool is available for iOS 4.1 which is required in order to unlock using Ultrasn0w 1.0-1 (Images Credit – TheApplePress).

IMPORTANT: proceed on your own risk. Do not attempt if you’ve not saved your SHSH Blobs!

WARNING: even if you have saved your SHSH Blobs, proceed on your own risk! Don’t do this if you ABSOLUTELY must rely on the iPhone 4 unlock!

You May Like to Check Out:

1. iOS 4.1 Direct Download links and Steps to Downgrade iOS 4.1

2. How to Jailbreak iOS 4.1 Beta on iPhone 3G & iPod Touch 2G

3. Sn0wbreeze 1.8 to Create iPhone 3GS 4.1 iOS Custom Firmware is Under Development.