This video shows a prototype of transparent smartphone that is being developed by a company called Polytron Technologies.
After seeing the video it looks like the real transparent smartphone is not that far off.
The only reason i think it would be useful is to use while walking without tripping or smashing into someone on road.
May be people will find more uses for it.
The one thing i can think of is not using the whole screen like regular phones. It could only uses the part it needs to show the info. Which intern could be a big saver on battery life. i don't know if only a part of the display can be powered or not.
But would be a good use of this tech....