The Trou Hologram cellphone has no screen, instead relying on 3D holograms projected onto the vacant area to display what you are looking at. Small projectors are lined up on the inner surface in order to bring the most lifelike images to life before your eyes.
They will have to figure out how to solve the power issues, since projectors suck a lot of energy. But one day we may just have this device in our hands fully working. That day is a long way away, but if we can envision it, we can eventually do it.