When I was a kid in the forties, nearly everyone had a part line. We could listen to conversations between people we didn’t know, or usually a person we had gotten to know through our parents having to ask them to give up the line in an emergency. It was considered impolite to not hang up after lifting the receiver and setting it on the cradle over three time. This usually meant you needed to make an urgent call.
As kids, when our parents were out after school, we could not resist the temptation to eavesdrop for a half an hour on a neighbour going on about so guys operation, what she was having for dinner or other juicy scintillating tidbits. We knew who was going to have a baby, a wedding or who had pegged out as one British man had said about his wife.
We could also listen on the extension in the bedroom to our sister’s conversations with her friends. We has to be extremely careful not to let her hear the click of the receiver being taken off the hook.