The Yotaphone is an extremely interesting idea. It combines a normal Android smartphone with a 4.3" 720p LCD screen up front and a 4.3" e-ink display on the back.
E-ink is extremely battery efficient and is the same basic technology used by Amazon in their Kindle range. The screen only uses power when the image being displayed changes.
Yota have a number of interesting uses for the e-ink display including notifications, updates on things like sports events and of course, as an e-reader. When used as an e-reader via their own app - it doesn't work with the Kindle app or any others yet - you select the book and page as normal on the LCD screen and then switch to the rear display by pushing an on-screen button. At this point, the LCD display powers down and you read on the e-ink display as normal. Swiveling the phone round switches the LCD display back on to the same page as you were just reading on the back allowing you to select text and share it in the normal way. This works really well.
Navigation around the device is very unusual with a touch sensitive panel beneath both screens and swipe and tap gestures for back, home and menu. It works quite well, but might take some getting used to. No standard Android soft buttons are on the display by default but they can be enabled on the LCD side.
The e-ink display is neither backlit nor touch sensitive unlike the newest Amazon Kindle devices, but it is still sharp and has enough contrast to make reading comfortable. The main benefit beyond that is the screen always being on and showing useful information when you pull the phone out of your pocket.
You can see our hands-on below, let us know your thoughts!