NEC Medias W I-05E launched a dual-display Android smartphone, that soon would be available in NTT Docomo network (scroll down for video).
Basically, the smartphone comes with two displays qHD (540 x 960 pixels) of 4.3-inch each that can be merged such that to deliver a nearly square tactile surface featuring a 5.6 inch diagonal. In other words, you can double the working surface or you can use the second display for your browser, gallery or other applications.
Tech site TheVerge noted that most applications run very well on both screens united as one and only some of apps can be divided to run simultaneously on each display.
Even if the two screens fold one over the other, the smartphone still has acceptable dimensions when closed: 12.2 mm in thickness and 64 mm in width.
NEC Medias W N-05E is due to be marketed in Japan as of mid-April, but for now there are no known details about price or availability on other markets.
Video: NEC Medias WN-05E, a double screen display