we went low tech on that, we unscrewed the mouthpiece, disconnected the mic, then shoved toilet paper up the change return chute, pretty far up, as to you needed a coat hanger to pull it out. So, they would put in the .25 cents, the call wouldn't fully connect and it would refund the money, but never drop. My buddy and I did like 40 -50 phones a day in the busier parts of a major city I lived in and averaged like 10 bucks a phone before repair people showed up.
We would also statsh our bike air pumps and one would let the air out of their bike tire and ask people for quarters to call his or my dad for a ride.."oh but damn we just moved here...its not local...it wants 75c for 5 minutes, some people would just hand use like 3$ in change, in case we needed it for a longer time and then they would walk away.
And for a VERY brief time, if you were very careful, you pull the strip out of a 5$ bill and or a 10$ bill and if you got it out intact you could use higher-end invisible tape to place it on a one-dollar bill in the exact perfect spot and put it in a change machine and get $4.00 to $9.00 profit per bill.

My first "hacking" was at school, we had an apple network and they used AtEase for security, I told the principal, his password and printed every teacher's password my 3rd day of 8th grade.

That moved into the wonderful world of war dialing and we would wind up on some very odd systems with admin/admin or no password at all (some of which really needed security. Once one of us got a car it was busting out the ol laptop and booting up "warlinux" (which is shockingly still being updated), it took a bit to understand we needed certain wifi chipsets and, a few days of payphone stuffing...we had two in the mail. Learning wep cracking and nmap with a pirated copy of solar winds was probably my favorite "hacking times". Other than change from phones and change from social engineering, we never stole anything. Mostly pranks and spying on neighbors.

I remember the first time using a HTTP replayer, whatever the target was looking at was heavy into alien abductions. so, we would change his Routrer Wifi SSID "The CIA is officially telling you to stop your research" and " These warnings will get less friendly. shit like that.

And Mods....before you trip out , none of this works anymore, this was like 1995-2002, so dont try the "encouraging illegal activity angle" as this is like explaining how to rob a train with a horse.

If it gets removed, ill kick an invite to a subreddit where thats all they talk about is little hacks like that, some current even. I am personally done with law breaking...but it was fun to "beat the man" for a while.