Unlock iPhone 3G, 3GS & 4 (iOS 4.0)
This works for the iPhone 4, 3gs, and 3g it is very simple it takes less than 3 minutes!
Unlocking your iPhone will allow you to use your phone on other networks that use sim cards. If you have a T-Mobile and you do not want to switch to AT&T then unlocking your phone is necessary.
The first thing you must do is jailbreak your phone (Click here to jailbreak for free). Once you Jailbreak your phone you need to open up Cydia and type in ultrasn0w into the search on Cydia. Download and instal Ultrasn0w and install it then your iphone will be unlocked.
Welcome to the iPhone community