Earlier quoted context omitted.
Was it literally just the sound of money dropping that validated the call? Presumably this was before automatic switching and a live operator had to connect you?
At one point it was. You could even record the sound on a handheld recorder and play it back. But it hasn’t worked in a long while. Pay phones mitigated this in a low tech way - by software muting the handset. Edit: oh yeah, and after that, you’d just call the operator and tell them the keys were sticky and to dial the number for you, then you’d “insert the coins” by playing the tones. Well, or you just third party b…
So does this mean that there was a dedicated second microphone hidden somewhere within the payphone body, that would continue to record the sound the coins made?