Was it ever actually possible to rip off a payphone that way?

Although I have never seen or heard of it being done outside this movie, I have to believe it was possible. Pay telephones relied on different tonal relays in order for them to work. When you dropped a coin into a payphone, you would hear certain faint high-pitched tones, sending the signal to the network that the payment for the phone was made, and activating the line for use. I would imagine that metallic contact of the connections could simulate the the "tonal" message, although I would have to believe that it would take a lot more effort to do so then shown in the movie. You'd probably have to play with it for quite some time to get the correct signal.

The way people were hacking at the time in this style was to use devices called Blue Boxes...or Black Boxes...or Brown..or Red...or whatever.

Each was a different design (built by yourself) which generated those specifically referenced phone system tones....of a specific frequency and in a certain order.

The most famous of this type of hacking...called phreaking....as in free speaking or phone free speaking.....Was capped Captain Crunch. He had discovered that the free whistle in capn crunch cereal could generate the 2600 hertz sound that some phone system used for access.

But the theory was pretty much the same with all of the hacks....know the frequencies the phone system was listening for (the world was totally analog) and then duplicate them.

One of the more interesting hacks I was told about was old push button phones...You know...the normal keypad 1-9, 0, #, *.....Well supposedly the military used a modified phone with e 4th column of buttons...And when many phones were made they had those buttons hidden under the plastic...you just had to screw open the case of the phone to get to the extra frequency generating buttons....barely a hack....

Many companies did that to save money with expensive electronic devices..they would build one style of device and put it in 2 different style cases for different prices. Like original single sided diskettes which could be made double sided with a hole punch or a pair of scissors.

I used to use a copper paper clip... go from the center of the mouthpiece (pin inside) to the lockbox keyhole.
Once connected, you hear the "clear" click and you could dial.

That was in NYC.

I've seen the boxes too... but never used one.

Check out the film Hackers. They utilize a similar hack.

MIT guys thought this up years ago.

I always thought that David was simply completing a circuit, that's all.

This is a Bell System 3-slot rotary dial payphone arranged for prepay service. This means it would be configured for ground start to get dial tone. The phone is connected by two wires (tip & ring) to the central office (CO). The ring wire is connected to one side of a line relay winding at the CO. The other side is of the winding is connected to negative 48-volt battery. So a ground on the ring wire at the payphone will operate the line relay. An operated line relay initiates a series of events at the CO to supply dial tone to the line. The payphone housing is always grounded to protect users from foreign voltages. Both the receiver and transmitter contacts in the handset are connected through the payphone’s internal wiring to the ring wire. So touching the grounded housing with one end of the pull-tab and the other end to the exposed transmitter contact would apply ground to the ring wire, and dial tone would be heard in the receiver. Ground is normally supplied through a pair of contacts that are closed when the hopper trigger is deflected by depositing a coin. The deflected hopper trigger also removes a short circuit across the dial contacts. Since no coin was deposited, the short across the dial remains and dialing would be ineffective. So, in this case, David would get dial tone but he wouldn’t be able to dial out.

I worked in communications in the Air Force. In the late 80's I was in a mobile unit while stationed in Osan Air Base, South Korea and I worked in a mobile telephone switchboard and a mobile message center. Think of small, square green vans on 4 wheels hiding under camouflage.
Anyway, when we were back in the dorms each floor had two touch-pad phones hanging off the wall. Somehow somebody gave me a secret code to call back to the U.S. without having to go through the Osan base switchboard(which was always busy and they only let you call back to the U.S. twice a month for 15 minutes at a time). Keep in mind this was via the military's telephone network, not commercial. I can almost remember the code: I think I'd press 9, wait 2 seconds, then press 4-7-8 and I'd get a dial tone. I could then call other bases in the U.S. in my case I would call Tinker Air Force Base switchboard operator and have them connect me to a local commercial number(Oklahoma city area). Once my girlfriend dumped me I didn't have the need for that secret code anymore!

Some people have testimony of this trick here:

https://groups.google.com/g/comp.dcom.telecom/c/weJ0FW0Njb4?pli=1

I've personally never done this. Phreaking in my day consisted mostly of tone generators and diverters. Toll fraud was big too.

Things like 'security' weren't a big priority back then for many governmental entities, corporations, phone companies and so on. Things were not very digital back in the day, so all these analogue signals and all the other very cheapest things the corporations could make work, were easy to phreak into, as they were so widely used.

If you research what phreaking was, how it started, watch the interviews of those people, maybe view some 'HOPE seminars' and such, you might start to get a pretty clear idea that it was actually SURPRISINGLY easy to do things like these, and many others this movie wouldn't show, because it would've looked too ridiculous.

If you were skilled, you could actually WHISTLE certain tones so the phone call would become free and so on, because it was all about tones and frequencies back in the day.

Though it is pretty ridiculous that a judge and jury actually BELIEVED Kevin Mitnick could whistle nuclear codes into a payphone and start World War 3, but that's how ignorant people were - and reading this board and these posts, people still are, sigh.

Please learn already, please?