I think 3-slots were around well into the 1970s, though single slots came out in the late 1960s. Single slots were first installed in more vulnerable locations, such as outdoor payphones or in public places. Payphones in say office building lobbies or semi-public phones in gas stations and luncheonettes got converted later.
But you're right -- they kept the coin-drop chimes long after the demise of that style of phone.
In the city, payphones for prepay, even if dial-tone first. (I don't remember if 3-slots could have dial-tone first). On TV, it seemed every pay phone was also pre-pay.
However, in rural locations, payphones were postpay. That is, you got a dial tone and dialed the number. If the line was busy or no answer you just hung up. But if answered you had to put in the dime to let your transmitter work. On such phones there was no "hold area" for coins and associated relay control, coins went directly into the box. That meant the phone had a much simpler construction as did the CO equipment, making it cheaper. People have previously stated there were ways to beat the system with that kind of payphone, but I presume the phoneco figured the cost savings were worth the risk, and maybe rural people were more honest and less scheming than city people.
Most people wouldn't know, just as non-computer people wouldn't notice the obvious fakery with most computer schemes shown on TV or movies.
In the film "Airplane!", the satire of disaster movies, they purposely used the buzz of a propeller plane as the background sound for the jet, among other sight and sound gags. BTW, the film was not original, it was actually a remake of a 1950s Canadian film. The original film was intended to be totally serious and they used almost all of its dialogue and plot. They just hammed it up and added some gag lines here and there. The original movie was already so overwrought it became funny pretty easily. (The original was shown on TCM who provided this explanation, the original never made it to video).
I saw an old TV show with Leslie Nielsen playing a cop. He did all the same earnest commanding lines as in "Police Squad" and "Airplane", only this time he was serious. But I couldn't take him seriously, I was laughing. Some actors become typecast in that mode that they have trouble doing other work. For instance, Don Adams (Maxwell Smart, a great phone user) always was seen as that character. On the Mary Tyler Moore show, the actor who played cartoonish newsman Ted Baxter likewise had trouble being taken seriously in other roles -- people thought he was still Ted Baxter.
Other actors make the switch ok. Jennie Garth was one of the 90210 spoiled rich kids and not a very likeable one. She's now doing a WB sitcom playing a very different character. (The new show uses an old fashioned cash register, FWIW).