iPhone 2G users are fairly disappointed these days as Apple has not provided iOS 4 for their devices. In WWDC, Steve Jobs declared that iPhone 2G is not capable of handling the requirements of iOS 4 firmware.
iPhone 2G will not get official iOS 4 update, but it is possible to get same iOS 4 experience on old devices. Mathew, an iPhone hacker, has created a custom firmware to bring some of the popular features of iOS 4 on iPhone 2G as well as iPod Touch 1G.

The custom firmware is said to be built on iPhone OS 3.1.3 and includes features such as Multitasking, iOS 4 wallpapers, Native MMS, USB and Bluetooth tethering, SMS count and many more features.
This custom firmware is still in its Beta version and will be available for public use soon. To install this custom firmware on iPhone 2G or iPod Touch 1G, you will need a special version of PwnageTool, called PwnageTool whited00r. The Beta version of whited00r tool is available for download on the official website (translated page).
iOS 4 Features on iPhone 2G
[via – iSpazio]

