Comment by dredmorbius

Pre-arranged times. Be there or else.

Payphones.

Time still exists. Payphones not so much.

And: payphones were ubiquitous. Car parks, bus stops, restaurants, bars, other businesses, random street corners, airports, bus depots, train stations. Probably several at a given high school at different locations. So long as you had loose change they were a reliable option. These started to disappear in the late 1990s, though support continued generally through the late aughts, and in certain locales (e.g., NYC) through the late 2010s.

There's some interesting technological anthropology in The Paper Chase, a film set at Harvard Law School in the early 1970s (released 1973), there is a payphone on the dorm floor, and it is the only phone available. That and a number of other elements date the film in ways that other set-dressing (costumes, architecture, cars) don't convey as emphatically.