Easy. Multi-line phone from years and years ago (1950's-60's). Running 4 pairs. wasn't common for homes back then, more so for businesses.
(and now, by answering that, I've really dated myself!)
My best friend in grade school's dad was a stock broker, and had multiple lines into their house... Was always fascinated as our house had the 4 plug ones, hers had the 8 plug ones (just like this) and a *very* cool phone with a push-button to go from the "house" phone number to her dad's "business" phone number. and IIRC the business line buzzed, the house line rang, and we were told *never* to answer the buzzer phone....