Have you ever wondered why old phone numbers started with letters? It’s a practice that seems strange to us today, but it made perfect sense back then.

On the iconic show I Love Lucy, when Lucy or Ricky Ricardo gave out their number, they’d say something like “Murray Hill 5-9975.” While this might sound odd to us now, it was a perfectly common way of sharing a phone number in their time. As Lucy would say, 'Lucy, you got some ‘splaining to do.'

In the mid-20th century, phone numbers included letters because of telephone exchanges—the systems that routed calls within a specific area. Every subscriber had a unique five-digit number, preceded by two digits represented by letters, indicating the specific exchange they were connected to. This system varied before the 1950s, with some cities using three letters and four numbers, and others opting for two letters and three numbers. Eventually, the standardized format of two letters and five numbers, or '2L-5N,' was adopted nationwide.

These telephone exchanges could only accommodate a limited number of subscribers—roughly 10,000 per exchange. Larger cities, therefore, required multiple hubs. For instance, the Ricardos’ number, MUrray Hill 5-9975, used 'MU' to identify the east side of Manhattan’s exchange. The 'Hill' part, along with the capital 'H,' simply served as a memorable label. This is also why we still see letters on modern phones (three above the digits 2 through 8, and four above the 9).

To assist customers in recalling telephone exchange names, full words were used, which proved easy for switchboard operators to understand. Using similar-sounding letters could cause confusion, so distinct names or phrases were favored. The words used to identify the two-letter codes were not standardized but instead were recommended by AT&T/Bell in their Notes on Nationwide Dialing, 1955 [PDF], which was distributed nationwide as long-distance calls became more frequent. A list of the names corresponding to each telephone exchange can be found here.

Around this time, area codes were introduced, but they were primarily used by operators rather than customers. In the late 1950s and throughout the following decades, the U.S. phone system shifted to all-number calling, which eliminated reliance on outdated telephone exchanges and allowed for the rapid addition of new customers simply by adding more area codes.

Despite this change, there was some resistance. Many people cherished the nostalgic charm of their old telephone exchange names, leading to the creation of groups like the Anti-Digit Dialing League and the Committee of Ten Million to Oppose All-Number Calling, which were formed to protest the change.

Can you believe it? People actually used to pick up the phone and make calls.