Blacksn0w RC2 To Unlock iPhone 3GS iOS 4 Baseband 05.11.07
Those of you who were able to jailbreak iPhone on iOS 4 can now unlock your device using Blacksn0w RC2. This unofficial release of Geohot’s unlock tool by the developer of PushFix, a fix for push notifications. He was also the same guy who gave us the Blacksn0w RC2 fix for iPhone 3.1.3.
As per the developer, Geohot has given his permission to redistribute blacksn0w. Blacksn0w RC2 is simply a repackaged version of Geohot’s original blacksn0w unlock for iPhone 3.1.2, 3.1.3 on the iPhone 3G and 3GS and hence it’s backward compatible with 3.1.2 and 3.1.3.
Along with the added support for the latest iOS 4, blacksn0w RC2 comes with fixes for some known issues including WiFi loss and boot loops. The current version has a bug which causes it to take up to 90 seconds to connect to the network after a reboot.
Note: Works only with iPhone 3GS on older bootroms, and baseband 05.11.07.
How to unlock iPhone 3GS iOS4 using blacksn0w RC2
1. First jailbreak your iPhone 3GS iOS 4.
2. Launch Cydia on your jailbroken iPhone and touch the Manage tab.
3. Then go to Sources –> Edit –> Add.
4. Now add http://cydia.pushfix.info as a source and touch ‘Add Source’. Let Cydia update your sources.

5. Once the sources are updated, search for ‘blacksn0w RC2 for iOS 4’ in Cydia and install this application.

That’s it. The app will automatically unlock your iPhone. You can use any carrier you like on your unlocked iPhone after reboot.
Thanks for this thread, just wanted to warn you to use the old blacksnow from blackra1n.com cydia source. It will fuck up the phone and you will need to go back to 3.1.2 and then 4.0 again.
I did this, what a fail.
thanks again