- You need a legit activated iPhone 3G S
- Disable 3G if you don’t have it
- Add apt.geohot.com to Cydia
- Install com.geohot.purplesn0w
- Watch for success output in Cydia
- Reboot
- Your iPhone is unlocked!
Why should you use purplesn0w? From George Hotz:
It’s a soft unlock for your 3GS that I’d actually use day to day. It’s not a daemon that takes any resources, and it doesn’t add a task to your baseband. It’s very close to a true unlock. All it does is patch three files, CommCenter, lockdownd, and your wildcard activation plist(which you need, activate w at&t sim first, no hacktivation support yet).
Remember to back up your data first before trying the unlock. To jailbreak your iPhone 3G S with purplera1n, follow the guide here
[image via QuickPwn]