iH8snow have released new their new Jailbreak for iOS 4.2.1 which covers all iDevices including the iPhone 4. Sn0wbreeze like all other releases allows you to create custom ISPW files to jailbreak your device, also included is basbeand presevation which means if your on 4.1 your can upgrade to 4.2.1 without updating your baseband meaning you can keep your unlock.
Sn0wbreeze 2.1 supports the following devices:
* iPhone 4, iPhone 3GS, iPhone 3G, Verizon iPhone 4
* iPod touch 4G, iPod Touch 3G
* Apple TV 2G
Ultrasn0w 1.2 unlocks iPhone 4 baseband 01.59.00 and iPhone 3G/3GS basebands 04.26.08, 05.11.07, 05.12.01, 05.13.04 and 06.15.00. If you are on any other baseband than these there is no current unlock for them so do not update and do not use this Jailbreak. If you are not sure about the unlocking do not update as there is no real need anyway
iPad and iPod Touch users are better off using Greenpois0n as you don’t need to preserve baseband like iPhone users
Please note that jailbreaking your iDevice may void its warranty so proceed with caution and at your own risk. Please don’t forget to backup your iPhone before you proceed