Planetbeing has apparently ported the Android to the iPhone. The Android OS is, in this video, apparently running successfully on the Apple phone.Hacker
Planetbeing has offered the Android-to-iPhone "pre-built images and sources" as a torrent download
For the time being, it looks like the porting only works on first-generation iPhones.
"It should be pretty simple to port forward to the iPhone 3G," says Planetbeing. "The 3GS will take more work. Hopefully with all this groundwork laid out, we can make Android a real alternative or supplement for iPhone users."
As Alexander Vaughn points out on AppAdvice, "Just like you can do Bootcamp on your Mac to access PC apps, you'll be able to go on Android to try all these apps that don't exist, or were not allowed on the iPhone."