I would say that there is a lot of comparison, between Android and Iphone, and a lot of points saying Android is better, or Iphone is better, bla bla bla.. But how about Android OS inside an Iphone hardware?
Recently, David Wong aka planetbeing from iphonelinux use OpeniBoot software to successfully dual boot Iphone OS and Android OS in an Iphone 2G. I believe he has done quite a lot of work migrating Android OS to Iphone hardware. If you look at the video, it seems like everything works out, and the dual boot seems interesting, you can have both OS inside your Iphone, and switch between them anytime you want.
According to planetbeing from http://linuxoniphone.blogspot.com/, the Android OS on Iphone hardware is still in Alpha stages, and it doesn’t work on some Iphone.
I am not an Iphone user, and I do not own an Iphone. But I really hope that one day a handphone maker, maybe HTC, Nokia, will launch a phone that support more than one type of OS, like maybe the user can choose between Window Mobile or Android, or even Iphone OS. The spec of handphone is increasing in terms of processing power and RAM, and another maybe is we will have Atom processor handphone, running Window 7, or a netbook running Iphone OS, just like Ipad.
Update (28 April 2010)
Step by step guide on how to install Android on Iphone here