I believe this was once used to connect heavy and clunky devices (called “tele-phones”) to wall outlets. They were called “jacks” or “johns” or something, and the point was to transmit voice via copper cable to other similarly heavy and clunky devices in other peoples’ homes. You had to “dial” a numerical code to get connected, but I can’t for the life of me figure out why they called it dialing.
I have always kept one of these spools around for an emergency; I think it’s safe to say that it would be a serious state of emergency if I needed a land-line. Unless I am starting a fly-by-night boiler-room telemarketing scam, I hope never to see this kind of wire again. We are at that point in history where the possession of a land-line telephone signals a line of demarcation between two very different types of people. You may draw your own conclusions thereof.
Of course, this telephone cord will have the last laugh when I am full of cancers thanks to cellular technology. There’s no app for that, is there.