Update iPhone 4 to iOS 4.1 Without Baseband Upgrade
Apple has released the iOS 4.1 which features a new baseband 2.10.4. If you update to iOS 4.1, you will lose the jailbreak and unlock. The latest Ultrasn0w 1.1-1 nor the downgrading back to iOS 4.0.x (with SHSH blobs) will not be able to unlock the iPhone 4. Notcom has found a way to upgrade to iOS 4.1 without upgrading the baseband to 2.10.4 and allowing you to unlock the iPhone 4 on iOS 4.1 as soon as the jailbreak for it is released.
Here is a simple step by step guide  to update iOS 4.1 while preserving the 1.59.00 baseband:
- Terminate all working applications.
- Download the latest version of TinyUmbrella (4.1.3) from here( Mac/ Windows/Linux) and launch it.
- Download the iOS 4.1 from here.
- Press the ” Start TSS Server” button
- After that launch iTunes and press restore (Not Update) your iPhone 4 to stock iOS 4.1. To do this, press and hold Left “Shift†button on Windows (left “alt†button on Mac) on the keyboard and then click on “Restore†(Not “Update†or “Check for Updateâ€) button in the iTunes  and then release this button.
- Now iTunes you the location select the location for your downloaded firmware file. Select that ipsw file and click on “Openâ€.
- iTunes will show 1004 error (baseband update failed). You do not have to worry because it’s part of the plan.
- Click on “Kick Device Out of Recovery†to bring your iPhone back from the recovery mode.
- Restart your iPhone 4.
It’s done. Be surprised to find your iPhone 4 working on iOS 4.1 with the old baseband 1.59.00!