Unlocking your 3.0 iPhone or iPhone 3G is super easy now – just turn off 3G (if you’re on T-Mobile US), open up Cydia, add their repo, and install ultrasn0w. Done!
First you’ll need to jailbreak your 3G or 3GS iPhone.
1. T-Mobile USA users should FIRST disable 3G in your Settings > Network settings before using ultrasn0w.
2. Add the repo repo666.ultrasn0w.com to Cydia or Icy.
3. Search for ultrasn0w in Cydia or Icy and install ultrasn0w and install it.
4. Reboot your iPhone 3G or iPhone 3GS.