Now, you can unlock iOS 4.0 Baseband 05.13.04 on iPhone 3G & iPhone 3GS with ultrasn0w 0.93. if you have jailbroken iPhone 3G/3GS 4.0 only then you can unlock iOS 4.0 with baseband 04.26.08 thru 05.13.04
We also posted about Unlock iOS 4 with Blacksn0w and Unlock iOS 4 on iPhone 3GS with Blacksn0w RC2 you should take a look at them! T-Mobile USA users must disable 3G before.
How to Unlock iOS 4.0 Baseband 05.13.04 on iPhone 3G/3GS
1. Jailbreak iOS 4.0 using Redsn0w, then start Cydia and go to Manage section.
2. Click on sources > edit to add following
Repo666.ultrasn0w.com (it’s ‘0(zero)’ and not ‘o’)
3. Do search for Ultrasn0w 0.93 and click on install
4. Let Ultrasn0w 0.93 to complete unlocking
and Bingo 😉