Flexible displays are already a reality on smartphones (even if they aren't exactly flexible in the real sense), and Samsung is already looking at innovative ways to make use of transparent displays, which are currently in development but will take considerable time to make their way to actual devices. A patent application of Samsung's describes how touch controls on the back of a device with transparent displays on both sides would allow for different functions to be carried out.
For example, touching the back of the device would let one open a folder from a list of folders, showing a preview of the content residing within the tapped folder; or, a touch on the back would make additional info pop up, such as a note, photo, and more, without having to navigate away from what's shown on the display on the front. Another nice example described in the patent includes moving two overlapping objects, one with a touch on the face of the device and one with a touch on the back.
Furthermore, other functions, such as controlling a video or drawing a pattern to unlock the device, are also shown, indicating Samsung has put quite a lot of thought into how transparent displays with backside controls would make the experience a more convenient one. There's no telling when we'll see smartphones with transparent displays crop up in the market, but whenever that is, Samsung will likely be a step ahead of other display makers, something that isn't exactly new for the Korean manufacturer. Hit the source link for more details on the patent.