Long story short: The lack of HW acceleration made the UI (and thus everything else) extremely sluggish. It wasn't even near usable for anything you'd like to do on a regular basis.
It was a good gag to confuse co-workers with though.
I think it can be done, since there was the android on iphone project. In theory, one would need to find the Linux kernel fork that was used at the time, treat it as "vendor" kernel and start the port:
Since then it doesn't really look like any progress has been made on running alternative operating systems on the iPhone.