You simply unfold and fold the device to gain access to any of the three interfaces which is one of the most intuitive ways to bring that functionality to a mobile phone. The standard interface is the mobile phone, if you unfold it to the left side you open the media player with scroll wheel and a larger screen while unfolding it to the right side opens the text messaging interface with a real qwerty keyboard and an equally large screen.

Nalu from DrppngMadScience and Vimeo.

Technically, Nalu is similar to a class of shapes known as flexagons (Nalu is one half of a tritetraflexagon to be precise). Flexagons have a discontinuous profile, with some parts being twice as thick as the other parts. Flexagons are normally made from sheets of paper, so you don’t really notice this. However, if you try to make a flexagon from anything thicker, you get a noticeably uneven profile.

Nalu gets around this by combining convex and concave shapes. As shown in the video, the center section is convex and fits inside concave depressions of the outer two pieces. This allows the design to have a flush and continuous profile. The thumb keyboard has a flat profile. The scroll wheel follows a continuous surface from the convex center part to the concave depression of the outer part. Magnets are used to hold the parts together.