I'd have thought that the big win market for an e-ink display is smart phones. The biggest problem with smartphones is the battery; an e-ink display should be m

I'd have thought that the big win market for an e-ink display is smart phones. The biggest problem with smartphones is the battery; an e-ink display should be much lower battery consumption than a screen. Plus, they're often used outside, where e-ink can (ahem) shine. A quick google turns up a few e-ink phones, but none of them seem really mainstream. Is there something I'm missing that makes e-ink sub-optimal for phones? (Thickness, perhaps?)