It's only working on a first-generation (2G) iPhone, and it's not quite fully functional, but the hackers at Linux on the iPhone have demonstrated a dual-booting iPhone with a working Android installation.
The developer says in the clip above that "pretty much everything works", although at an "alpha level". Next up is the iPhone 3G, followed by the harder-to-crack iPhone 3GS and the next iPhone hardware you might have heard about. The next big thing in jailbreaking may just be Android access. [Linux on the iPhone via Boy Genius Report]