@bondsbw: I'm sure we'll learn more details as the Summit continues.

But it seemed as though all you needed to do was add support for the smaller screen and maybe tweak the UI to be better for the phone. If I had to guess, I'd bet that a C#/XAML Win8 app would run on WP8 with no changes, but it might look a little weird. And, of course OS-specific things like the snap view, charms support wouldn't exist on the phone.