The first telephone book had 50 names in 1878. It was issued on February 21 by the District Telephone Company of New Haven, Connecticut, soon after the world’s first commercial telephone exchange began operating there.
This pioneering directory was not a bound book like modern phone books. It was a single cardboard sheet listing the company’s subscribers, including private individuals, businesses, and offices. It also did not provide telephone numbers: callers contacted a switchboard operator and asked to be connected to a subscriber by name.
The New Haven exchange opened on January 28, 1878, with only 21 subscribers, but the number had grown to 50 by the time the directory was published. A common mix-up concerns a later New Haven directory issued in November 1878, which was a fuller booklet containing 391 names and addresses. The famous answer of 50 refers to the first directory, not that later expanded edition.