> Horrible idea now as the phone systems would easily record the number that called it

I think the idea was that you'd be calling from another pay phone, probably a different one each time so the number didn't matter.

You could do the same with pagers. Your drug dealer would own a pager, you'd call the pager from a random pay phone and send that pay phone's number as a message. The dealer would then use a different pay phone to call you back.

Unlike cellphones, pagers were often one-way, receive-only devices, so you couldn't use them to track somebody's location.