Starting from iOS 4.0, Apple completely cut off the support for aging original iPhone EDGE and iPod touch first-generation. Their decision of course was justified because of the low RAM found in these first-gen devices which were released back in 2007.
While iOS 4.2.1 is still available for iPhone 3G and iPod touch 2G, they are barely capable of running it, and that too without the goodness of multitasking, wallpapers and Folders.
But all is not lost as the iPhone jailbreak community has now come up with a mod, which brings the complete look and feel of iOS 4.2.1 for iPhone 2G, 3G and iPod touch 1G and 2G. The mod is basically based on the iPhone OS 3.1.3, to replicate the experience of iOS 4 on the first and second generation iPhone and iPod touch.
This custom firmware, dubbed WhiteD00r, includes everything from: wallpapers, new semi transparent dock (and UI), backgrounds, all new icons from iOS 4.x, Voice Control, multitasking, video recording, and more.