Adam Pash, Lifehacker's editor-in-chief, did it with an iPhone 3G, but it might be possible with an iPhone 4. Like everything, there is a catch; you'll have to jailbreak your iPhone.
Once the Droid OS is installed, Lifehacker describes the frankenphone's performance as "occasionally a little laggy," but overall, Pash is pleased with his creation.
And yes, that is a Droid robot holding an apple in the photo. Subtle.
The iDroid hack wouldn't be complete without detailing how to use the four-button Android operating system on the nearly buttonless iPhone. (Lifehacker obliges.)
But if you really wanted to run the Droid OS, why not just buy a Droid phone? After all, commenters imply apps in the Android Market are off limits to iPhone users.
Still, this could be practical for app developers and rabid tech junkies looking to impress their friends.