[TOMT]B&W movie 1930-1940 investigation uses sound of rotary phone over speaker to deduce phone # called.

Hoping a film aficionado might be able to help: I remember seeing a movie made (guessing) somewhere between 1930 and 1949 -since it was filmed in black and white. There is a scene where an investigator and I believe a woman are listening to the sound of a rotary phone being dialed over the venue’s speaker or PA system in order to figure out the number being called. That is about all the detail I can give you. TIA!