First, this does not make much sense unless you are someone who just wants to try out crazy stuff. Somehow I was in an unstable mode that day and jumped right in when I saw this article that details all the steps how to run Android 2.2.1 on iPhone.
And it turned out to be a disaster and waste of time.
The installation process all went fine. And I can boot into Android, though the boot process is a bit long (maybe because mine is iPhone 2G?)
After booting into Android, everything looked fine, except that I could not find the Market to download apps -_- !!!
I played around with existing apps. The camera is not really working and crashed several times on me. The phone dial seemed to be working fine and I can make phone calls.
Then I got bored and booted back into iOS. To my surprise, iTunes cannot recognize the iPhone anymore. This means I cannot sync and do backups, which really really sucks. The tutorial should have warned me in advance.
Another strange thing is that many settings are changed in iOS. All the name in my contacts are gone, so basically I only see the phone numbers now. Also settings like screenlock, wifi and others are also changed somehow.
I tried to restore and jailbreak again. It took me quite some time to find the right firmware and tool. Finally, everything is back to normal and data was restored.
So, I highly discourage this experiment to anyone since the software is still not stable.