The old telephone trick

It was possible to hear the faintest whir of the dial, he knew, but he couldn't accept the probability that Harsh could discern the number he dialed. He had often heard rumors of smart operators who claimed to be able to recognize a number by counting the clicks, but he had yet to meet such a man. He had, in fact, wasted several weeks when he was much younger trying to train himself to do the trick, and had given up in disgust. No, Harsh could not have learned Lucy's number that way.

(from This Is It, Michael Shayne, by Brett Halliday)