How Does It Work?
The first thing worth mentioning is that Android on iPhone isn't close to ready to use as your full-time mobile operating system. That doesn't mean it never will be, but at the moment, this is more something you'd want to do to fulfill your curiosity, wear as a geek badge, or just have a little fun and (maybe) support a really great project.
You can see how far they've come along with each phone on the iDroid status wiki. As I mentioned above, the iPhone 3G is the best supported iOS device (and currently only it and the 2G work with the method above, I believe). The biggest issue right now with the 3G is power management (PMU on the wiki), which isn't fully functional. Most importantly, suspend isn't yet working, so your battery won't likely last long. It's still come a long way from where it's been in the past, though, and having followed this project excitedly for a while, the progress they've made in recent weeks has been really impressive.
Regarding a few nuts and bolts: Your iPhone's lock button acts as the Android back button; the iPhone home button acts as the Android menu button; the iPhone's volume down button acts as the Android home button; and the iPhone's volume up button acts as... I'm not really sure what. To lock the screen, press the iPhone's home and and lock buttons at the same time. To power off, hold the lock and home buttons for a couple of seconds until the Power Off prompt appears. You can see a few other operating quirks by watching the video above.
As you can see in the video, performance isn't perfect (it's occasionally a little laggy), but again, with time, that could change significantly. Either way, the iDroid project—along with OpeniBoot and Bootlace—is something I remain extremely excited about. As a long-time iPhone user and recent Android switcher, the main thing that sets the two apart for me is the iPhone hardware, which always feels a head and shoulders above whatever Android device I put my hands on. I know a lot of people (including myself) who'd kill to dual boot and iPhone 4 with iOS and Android. (In fact, if you really want to help out, you can donate to the iDroid Project by clicking the Donate button on the top right of the iDroid Project's main page and maybe speed things along.)Read more at lifehacker.com