Unlock iPhone 4 on iOS 4.1 with Ultrasn0w [How to Guide]

How to upgrade to iOS 4.1 while preserving your baseband 01.59.00

STEP 1: Download TinyUmbrella latest version from here and iOS 4.1 for iPhone 4 from here.

STEP 2: Close iTunes & connect your iPhone 4 to your PC then launch TinyUmbrella and select “Run as administrator”. If you got a Windows Security Alert, check both boxes and click on “Allow Access”.

STEP 3: Hit “Start TSS Server”. While the TSS Server is running well, TinyUmbrella will kill iTunes.
STEP 4: Now launch iTunes and click on the iPhone icon at the left sidebar of iTunes then hold left “alt” button (“Shift” button on Windows) + Shift from the keyboard. Point it to the iPhone 4.1 firmware you already download.
STEP 5: iTunes will go in a bunch of steps to restore your device to iOS 4.1, it should give you error 1004 which indicates that the baseband is preserved successfully.

STEP 6: Get back to TinyUmbrella and hit “Kick Device Out of Recovery” to get your device out of Recovery Mode. let's unlock!

How to unlock iPhone 4 on iOS 4.1 baseband 01.59.00 with Ultrasn0w

STEP 7: First, you will need to jailbreak your device using Limera1n jailbreak tool from Geohot by following the step by step guide posted here.

STEP 8: After jailbreaking, open Cydia and touch on Manage >> Sources >> Edit and hit the Add button on the top. Type http://repo666.ultrasn0w.com then hit “Add Source”.
STEP 9: After installing the repo, go back to Cydia and search for Ultrasn0w, tap on it and it will be installed automatically.
Well done, now you got iPhone 4 totally jailbroken & unlocked on baseband 01.59.00, congrats. We will be happy to hear your questions about any issues or problems facing you while following the guide.