It's already stepping on the toes of Amazon's dual-display patent, but at IFA e-ink is showing off a prototype handset featuring a traditional full colour LCD panel on the front, and a dull monochrome e-ink display on the back. Kind of like a reverse technological mullet with the party in the front and business in the back.
E-ink displays still have some distinct advantages over LCD and OLED technologies -- namely their insanely great battery life and perfect readability in sunny conditions. So having a backup display that can still operate when a handset's battery is nearly dead could be neat. But without touchscreen functionality of its own, which is tricky to implement on a dual-sided phone that's always being touched, it's almost useless. Still, E Ink claims there's already manufacturers interested in making something like this, so for better or worse expect to see such devices popping up in the coming year.