unlock to work. The iPhone 3GS (running iOS 5.0.1.) is supported with the following basements: 04.26.08 – 05.11.07 – 05.12.01 – 05.13.04 – 06.15.00. The iPhone 4 is supported if your baseband checks in as 01.59.00. If you're looking to upgrade from a dustier firmware, make sure you preserve your baseband before unlocking. Hit the source link for a few tips, and remember: friends don't let friends jailbreak before completing a backup.