Rest area payphones. Its why most rest areas have a huge blown up atlas map these days
edit: and as a note, the death of the rest area payphone is a huge problem some places. you ever look at a coverage map for west virginia? you break down or get lost out there and you're totally fucked
This is actually a map of the Netherlands and I'm from there. I'm also old enough to remember a time without mobile phones. This was probably the call centre for triple AAA, in Dutch the ANWB. We had these emergency telephone poles along the highways. When stranded and without a map you could easily call aid through them with these phones, which they also knew where they were, for easy dispatching.
I'm also dutch, and Im pretty sure you couldn't call for route advice from the ANWB poles. Or at least, you couldn't in the later years, maybe it was different in the 60s.
It does make a lot more sense these people are planners, not general navigation advisers.