Apple today released iOS 4.2 GM for developers and guess what? iOS 4.2 is vulnerable to Redsn0w 0.9.6 b2 released by iPhone dev team. You can jailbreak your iPhone 3G, iPhone 3GS, iPhone 4, iPod Touch 2G, iPod Touch 3G, iPod Touch 4G and iPad running on iOS 4.2. Needless to mention but if you use Ultrasn0w to unlock your phone should stay away from Apple Stock Firmware update and Redsn0w.
Current version of ultrasn0w unlock works for all firmware from OS 3.0 up to iOS 4.01, for more information check ...