party line

noun, a telephone line shared by two or more subscribers (COD)

“Sarah Smith operated the party line, which I remember. I remember picking up the phone and you could just listen in, but so was everybody else.”

“I remember we used to be on a party line.”

“We had one phone, and it was a party line. So you basically knew what was going on in the neighbourhood. All the rings would come in. They knew our business. We knew their business.”

“We had telephones. Remember the party lines? There’d be five or six people on each line, and if you picked it up there might be somebody talking.”
“Couldn’t always tell that somebody was listening in, right?”
“No. And some people’s hobby was listening on the party line.”