Earlier we discussed how to unlock iPhone on iOS 4.0. In this tutorial we will outline the similar steps (as jailbroken iOS 4.0.1 is 
To be able to unlock your iPhone on iOS 4.0.1 you first need to jailbreak it.
Once it’s jailbroken, proceed with these simple steps to unlock your iPhone 3G to be able to use any carrier sim card.
1. Run cydia on your iPhone 3G
2. Goto search option on right bottom
3. Search for ultrasn0w (its zero, not O) – it will be version 0.93 [there is no need to add repo666.ultrasn0w.com to cydia, as it is already included in the redsn0w 0.9.5 beta 5 build 5]
4. Install ultrasn0w version 0.93 from cydia
5. Restart your iPhone and voila!
This will unlock your iPhone 3G to use any cellular network provider sim and not only your default carrier (Which is AT & T usually)