How To Unlock iPhone 3G on 4.1

this is the guide which you can use to unlock iPhone 3G, on iOS 4.1, using Ultrasn0w. The following guide can be done only on a jailbroken iPhone 3G, with iOS 4.1 installed. These steps only require few minutes and are simply to perform. Be sure to follow the steps as told, and do not stray on any other paths. At the end of this guide, you will have an unlocked iPhone 3G. That means you can use any SIM cards and choose any carrier you like, giving you the flexibility wanted.
iPhone 3G unlocked
Update: I see a lot of you having trouble with this so, I wrote a new one. Follow the steps here. They will first take you to jailbreak iOS 4.2.1 ( follow the link in the first paragraph of the new guide ) and then, straight to unlocking.
How to unlock iPhone 3G on iOS 4.1

Start Cydia from your springboard.
Touch on the “Manage” tab, located on the bottom of the screen.
Cydia Screen
Now touch on “Sources”.
Touch on “Edit” and then on “Add”. In the box shown, you must type this url: http://repo666.ultrasn0w.com and the touch on “Add Source”, like bellow:
The type box
After Cydia has finished to update the sources, search for “ultrasn0w 1.0-1” in the Cydia screen. By installing this application, the unlocking process will begin.
After Ultrasn0w has unlocked the device, simply restart it and you’re done.