You can date a movie by the cars, the clothes and hairstyles, or by the telephone technology. I seen recent movies that depend on texting and older movies where the plot depended on an inability to reach someone on the move. There are even older films, like the gripping "Sorry, Wrong Number" that turn on the availability of a human operator. It's fun to watch, and to remember the old days.
How many people today know why there are no letters on the dial -- sorry, I guess they're all keypads now -- for 1 and zero? The answer derives from the fact that early phones connected to a central operator by lifting the receiver and creating a click. More here. When direct dialing was introduced, and the system worked by the number of clicks, not the different tones on modern phones, a single click was reserved for reaching a trunk link or an operator. The exchanges were built around names using the first two letters -- hence PEnnsylvania 6-5000, the Glen Miller song from World War II. Over time, phone numbers expanded from 6 to 7 to 10 digits. As recently as the 1980s, I had a weekend cottage served by a small rural telephone company that let us call anyone local by dialing only four numbers. You could also choose between private [individual] and "party" [shared] lines, where you could listen to your neighbors, and they to you, and new calls could not be made until the other party ended their call.
Another difference between now and then was the high cost of long distance calls. Many families had little 3-minute egg timer hourglasses by the phone so that they would keep their holiday calls to family members short. When I first started working in Washington, I would drive to work on weekends in order to use the office WATS [wide area telephone service] line for calls to my parents in Denver. Now we can have Skype video calls almost anywhere in the world for the price of an out of state call four decades ago.