In junior high we learned this trick to make free calls on a pay phone. First, you needed to short the low-voltage phone current by bridging the metal in the microphone of the hand set with a ground, usually the master screw on the faceplate of the phone. A straightened paperclip was ideal for this because you could just stick one end in the small holes of the speaking part of the handset, and touch the other end to the screw. You could hear a scratching noise when you made the connection.
Once it was shorted, you could dial your destination number by tapping the hook (the thing you hang the handset on when you’re finished). You’d just tap out your number: tap-tap-tap for number 3, tap-tap for number 2, etc. Timing was important because if your tap was too long, your call would hangup. Long numbers like 8 or 9 were a nuisance, but at least we only had to tap out 7 digits in those days.
This technique worked like a charm every time. The only challenge was getting a wire to make the electrical short. I remember scouring the ground looking for material. A bobby pin would work, but you had to scrape off the plastic on the tips. In a pinch, you could even peel the foil of a gum wrapper and carefully roll it into a wire. Sometimes we just carried a paperclip for the purpose.
I’m sure I even called my parents a few times this way, and they had no idea I was engaged in an outlaw anarchist phone phreak political act. Heck, I thought I was just saving 10 cents.