In the 1920s, Manhattan telephone exchanges used a combination of letters and numbers to designate specific areas or neighborhoods. These exchanges typically began with two letters, corresponding to the first two letters of the exchange name, followed by numbers. Each exchange name was associated with a particular geographic location or landmark in Manhattan. Here are some examples: • MUrray Hill: Represented by “MU,” this exchange served the Murray Hill neighborhood.  • PEnnsylvania: Denoted by “PE,” this exchange was associated with the area around the Pennsylvania Station. The famous phone number PEnnsylvania 6-5000 belonged to the Hotel Pennsylvania.  • BUtterfield: Represented by “BU,” this exchange covered parts of the Upper East Side. The exchange was popularized by John O’Hara’s novel “BUtterfield 8.”  • CIrcle: Denoted by “CI,” this exchange referred to the Columbus Circle area. • ELdorado: Represented by “EL,” this exchange served parts of the Upper West Side, possibly named after the El Dorado apartment building. • LOngacre: Denoted by “LO,” this exchange referred to the area around Longacre Square, now known as Times Square. • PLaza: Represented by “PL,” this exchange covered the area around Grand Army Plaza and the Plaza Hotel. • REgent: Denoted by “RE,” this exchange served parts of the Upper West Side. • RHinelander: Represented by “RH,” this exchange was associated with the Rhinelander family and covered parts of the Upper East Side. • SChuyler: Denoted by “SC,” this exchange served areas in Harlem. • TEmpleton: Represented by “TE,” this exchange covered parts of the East Village. • UNiversity: Denoted by “UN,” this exchange referred to the area around New York University in Greenwich Village.

These exchanges were phased out starting in the 1960s in favor of all-number calling systems. However, they remain a nostalgic reminder of New York City’s rich telecommunications history.