This would be simple really
most phones nowadays have integrated cameras, and many phones have screens on the exterior
This would have to be a clamshell design phone with a large color outerscreen covering the entire front section of the phone, covered by a non-reflective durable transparent plastic
sheet. On the back, a camera that projects everything behind the phone to the screen on the front. thus, creating an see through/invisible-type illusion when looking at the phone head on.
It would blend into its surroundings in a cammouflage sort of way
The only real benefactor of this, aside from the novelty aspect is that a neglibable amount people would notice it, making it inconspicuous, and less of a target for thievery and other evil phone related wrong doings.
i wouldnt buy this though, im generally quite happy with my simple, non technologically advanced mobile with none of this futuristic nonsense. And I must say again, I'm a real fan of my 'Pokia' (linked)i use it all the time at home. its cool as shit.