How to Unlock iPhone 3GS 3.1
This step-by-step guide and tutorial will show you how to unlock your iPhone 3GS running OS 3.1 using UltraSn0w. This is a very simple method that requires only a few steps.
Step 1: You have to jailbreak your iPhone 3GS by following one of these tutorials.
Step 2: Once jailbroken, follow these steps:
Launch Cydia.
Add the following source to Cydia repo666.ultrasn0w.com (note there is a “0″ in sn0w, not an “o”).
After installing this source in Cydia, search for “ultraSn0w”.
Install UltraSn0w and reboot your iPhone.
Tha’ts as simple as that!