These are instructions on how to jailbreak and unlock your iPhone 3G on iOS 4.2.1 using PwnageTool 4.1.3 for Mac OS X. This tutorial will explain how to upgrade your baseband if needed for an unlock.
Step One
Make a folder called “Pwnage” on the desktop. Download a couple of things:
If you are on the 05.14 or 05.15 baseband you will also need the iPad 3.2.2 firmware. You can find out your baseband version in Settings -> General -> About -> Modem Firmware.
Sn0wBreeze 2.9.6(pwnagetool for windows, supports untethered jailbreak of iOS 5.1.1 for iPhone 4, iPhone 3GS, iPod Touch 3G, iPod Touch 4G, iPad and Apple TV 2G)
Sn0wBreeze 2.9.3(pwnagetool for windows, supports tethered jailbreak of iOS 5.1 for iPhone 4, iPhone 3GS, iPod Touch 3G, iPod Touch 4G, iPad; untethered for iPhone 3GS with old bootrom; untethered for iOS 5.0.1, iOS 4, iOS 3 supports Apple TV 2G)
Sn0wBreeze 2.8b11(pwnagetool for windows, supports iOS 5, iOS 5.0.1, tethered jailbreak for iPhone 4, iPhone 3GS, iPod Touch 3G, iPod Touch 4G, iPad, Apple TV 2G; untethered for iPhone 3GS with old bootrom)
Current version is ultrasn0w 1.2.3, download in Cydia (unlock for iPhone 4, iPhone 3GS, iPhone 3G, firmwares 3.0-4.3.3; it supports basebands 01.59.00, 04.26.08, 05.11.07, 05.12.01, 05.13.04, 06.15.00)