Any device these days gets hacked and fooled around with. The iPhone is of course no exception. Developer David Wang hacked an Android OS version to boot on the original iPhone.
The iPhone actually has a boot loader to either boot iPhone OS or Android.
The Android OS comes up, but overall the quality of the port is alpha says Wang.
He says that a port to iPhone 3G should be straight forward. To make Android work on the current 3GS is supposedly taking more effort.
Besides the coolness factor of owning an iPhone that runs Android I do not see much use. More details can be learned in the video below and on this blog.