An unknown group of hackers work now on bringing current beta version of iPhone OS 4 to the iPhone 2G (that was released in 2007). As you remember, Steve Jobs mentioned on his iPhone OS 4 keynote that the system won't be supported by iPhone 2G due to its low memory and processing power. Hackers also explained what they are working on:

"We are rewriting the 4.0 beta firmware released by Apple to create a custom firmware that can run on devices iPhone 2G which is no longer available. To do this we studied the architecture of the firmware previously released by Apple on the device trying to understand how is it different from the released versions on other devices, in particular that of the iPhone 3G device, which is what most resembles the smartphones".

According to a shady photo above they've already reached success but still there is no relevant information revealed on their site ^[1].