In what decade was the # symbol added to telephone keypads? The answer is the 1960s.
Touch-tone telephone keypads were developed by Bell System engineers in the 1950s and introduced commercially in the 1960s. The familiar keypad included the digits 0–9 plus two extra keys: the asterisk (*) and number sign (#).
The symbols were added for specialized telephone services and computer-controlled systems, not because people were already using hashtags. The # key later became widely associated with menu navigation, voicemail commands, and automated phone systems.
A common mix-up is assuming the symbol was created for social media. Twitter popularized hashtags online in the late 2000s, but the character had already been part of telephone keypads for decades. Its telecommunications name was generally “number sign” or “pound sign,” depending on region.