Here’s How You Can Update iPhone 4 on iOS 4.1 Without Upgrading 1.59.00 Baseband to 2.10.4

The final version of iOS 4.1 features a new baseband 2.10.4 which is currently not supported by Ultrasn0w 1.1-1. If you update your iPhone 4 to iOS 4.1, and then later downgrade back to iOS 4.0.x (with SHSH blobs), you still wont be able to unlock your phone as the downgrading of firmware wont downgrade your baseband, hence making it impossible to unlock.

The following step by guide will enable you to upgrade iPhone 4 to iOS 4.1 without upgrading to 2.10.4 baseband. This method assures that your iPhone 4 on iOS 4.1 is on the older 1.59.00 baseband which will enable you to unlock your phone as soon as the new jailbreak tool for iOS 4.1 is released.