In the early days of telephony, exchanges consisted of banks of operators at switchboards. Subscribers would pick up their phones and a light would illuminate on the board of one of the operators. She (as it almost invariably was) would plug one end of a cord into the hole by the light, connect her headset and ask: “Number please?”

For a local number, she would plug the other end of the cord into the hole representing the destination number to make the connection. For long distance, the operator would plug into a trunk circuit connected to another bank of switchboards elsewhere.