Off the top of my head, I would suggest:
-- restaurants that do a lot of take-out or delivery business (pizza places, Chinese/ethnic restaurants, lunch places in financial districts of major cities). When people want delivery food, they need a menu on-hand.
-- restaurants near colleges/universities. High usage of smartphones, lots of eating out.
-- restaurants in areas with particularly high smartphone market penetration (Bay Area, New York City, Boston, Seattle)
A good menu/take-out order system for restaurants is something I've been thinking about on and off since I was in grad school (and that's been cough over a decade now).