Sn0wbreeze 2.2 is now available for download. It can jailbreak iPhone 4, 3GS, 3G, iPod Touch 4G, 3G, 2G, and iPad on iOS 4.2.1 Untethered by building custom IPSW firmware while preserving iPhone baseband.
Sn0wbreeze 2.2 is the Windows equivalent of PwnageTool 4.2, a Mac OS X only program. This version includes the ‘Baseband Preservation Mode’ which lets iPhone 4 users preserve their baseband while restoring to custom iOS 4.2.1 firmware.
Simply follow the step by step instructions in the video embedded below to create custom 4.2.1 IPSW file without the upgraded baseband to jailbreak your iOS device.