I confronted the owner of this "system" and using all your information as ammo I finally pried it out of him that he bought it at Target in the late eighties. It was an early attempt to market a feature rich phone system to the home owner-work at homer without buying a complex and of course, expensive key system. It is a wired system where all sets are wired to the same T and R and the 1050 set controls the 1020 sets. I told him the year was 2016 and referred him to the Internet and suggested he look for wireless home phone systems with speakerphone, intercom, paging, answering, etc.

Forty six years and still fascinated with Telecommunications!