Forgetting WP? And even Android? Can you go out, buy a Lumia, and install a working copy of Android?
You can install Android on devices that are already running some version of Android. And some fringe cases like the HTC HD2 and HP Touchpad (I had both, the Touchpad didn't work too great). But that's far from what the OP was asking for.
What you are saying only applies to iOS really.