Well, one could imagine a purely visual phone book, which contains a photograph of every person in town, as compared to a text-based phone book, which has every person in town listed by name.

The photo-based system would no doubt work great if the town had only a dozen people (all of whom know each other by sight), and probably work acceptably well for up to a few dozen. It's going to suck for a town with a thousand people, though, and be utterly unusable for a city of a hundred thousand.