Design studio Alloy have developed a prototype mobile phone called the Polygon, which features a dual-screen display similar to the Nintendo DS.

According to Alloy:

"The resulting concept Polygon has a familiar 'phone' size and form-factor, but open the flip and you will find two screens. The first screen is large and high resolution, optimised for watching television pictures. The traditional keypad is replaced by a second screen that is a tougher, lower resolution touch screen. This acts as the user interface, changing according to the context of use and allows the device to be viewed both portrait (phone, MP3 player) and landscape (TV, web browser)."

[Source: Alloy, via Textually.org]