Can we install Android on an iPhone 4?
The short answer is no.

At the moment, most of iPhone 4 hardware is unsupported by iBoot. The thing is that iPhone 4 bootrom hasn't been hacked in order to install custom boot loader that will boot Android and, as I said before, many of iPhone 4 hardware has no drivers.

Also, iDroid allows you to install only 2.x at the moment. However, I have asked the devs some time ago, they told me that they're working on porting Android 4 to the iPhone 4.

Anyway, until there are a needed bootrom hack (which also leads to untethered jailbreak, pod2g/Chronic can release it soon) and quite enough drivers you won't be able to install android on your phone.