Just arranging it the last time in person. Mail worked just fine to confirm or cancel a bit before since the same city. If you needed things more quickly, couriers was one way. There were also a lot third spaces and people met out and about more and more often. They might see each other every Sunday at the same church for instance.

Up until I was in uni, even payphones didn't matter most of the time since there's no guarantee both parties are going to be near one and no normal person had a pager. If you were going to a business that had a phone, you could look up their number and call them to put one of your buddies on the line or at least send a message (see the running gag on the Simpsons where Bart calls the bar to ask for someone).

We also just waited a bit and if they didn't show, we went on with our plans.