iPhones.ru posted a video (with dialogue in Russian, I think) showing a first-generation iPhone that's been modified to light up the Apple logo on the back of the device when it's turned on.
Sadly, it doesn't show how exactly the modification was made, though I conjecture it uses light from the main display somehow, perhaps with optical fiber. Maybe the presenter is discussing it, but I don't speak Russian, so it's hard to say.
It looks pretty cool. I'm old enough to remember when people were doing this to their PowerBooks, so who knows? This might just be a built-in feature of some future iPhone.