For me, a full blown tablet is nice real estate wise, but it can be tedious to type on. By contrast, a smartphone is nice and handy for thumb pecking out email and posts to Facebook, but the screen is so darn small. Would there could be something in the middle which would offer larger screen real estate, but not kill the battery and still let me type on the go.
Enter the Sprint Kyocera Echo. The Echo is an interesting dual screen smartphone, with twin 2.5” WVGA screens which separate thanks to an ingenious hinge, allowing for single screen phone use or dual screen tablet mode (where it stretches out to 4.7 inches square). And I have to say that the hinge had me a bit worried when I read about it. I had this ugly image of the hing breaking after a few months use, leaving angry users stuck with an expensive repair or replacement bill because they aren’t eligible for a new phone. But Kyocera has made the hinge design pretty robust and after a few months of daily use, it isn’t even lose. Hats off for making a tough design.
(from reviews) 
