Yes, it has been done finally. Planetbeing has published a video showing the Google’s OS dual booting on Apple’s original iPhone using the DualiBoot loader.
Though the Android OS is not completely functional but you can perform the basic functions easily. Currently this hack is only for iPhone 2G/3G and Planetbeing has already started working on iPhone 3GS.
How to Run Android OS on iPhone?
If you want to give it a try, you can visit the blog of original author for more details and documentation with download link.
Video Running Android on iPhone: