On the other side - A flashlight

Imagine you're sitting on your sofa watching a good movie a late Friday night. Then suddenly, a "click". Everything turns dark. Your TV, your room, and all the street lights outside. It's a major power outage. You can't see anything really. Luckily you have your mobile device in your pocket as usual. You slide up the backside face of the mobile device and turn on the built-in flashlight. Your room lits up, and you can navigate in your apartment.
In an earlier post, I argued that it was a pity that the IPhone only uses half the space available. One side is full of goodies, while the other side is just an empty space of plastic - useless. So, since the backside of the IPhone gives no value at all to the user, then anything that adds value would be infinitely better (mathematically speaking, that is). Your mobile device is a thing you carry with you all day long. Why not put as many usages as possible to it since it's available all the time? Maybe it would feel kind of dorky to have a built-in flashlight in your mobile device. But I think you'd appreciate it in the scenario described above. In an other post, I came up with the idea of having a built-in recordable mirror on the backside. I guess that would attract the vain mobile users of the world. But what do I know, I'm just thinking out loud.