It's something that can look pretty cool and futuristic and I'm sure we'll get there, but I'm not sure this is very practical. As you pointed out, the only real practical application would be augmented reality, but I think that's better suited for other devices, not smartphones.
What could drive this technology beyond a gimmick for me would be if the smartphone could become opaque too on command. So when I need it to be a regular smartphone with vibrant colors that has a display pointed at me and not everybody around me, it could be that, but when I want it to be the futuristic augmented reality see -through thing, it would be that as well.
Another big problem with see-through smartphones would be using them outside - it the sun is in front of you, you are going to have to forget about seeing anything as looking at your smartphone at certain angles would also mean looking at the sun.
Yes, you make a very good point. A transparent phone would need to be able to turn opaque on command to be of real use as a display where you are the only one consuming the content on the phone.
Yep... But I think the technology to turn something transparent into something opaque actually exists already. The question is if it will pair well with this see-through display too.