I have one that I got in 1982. Haven't used it in 20 years. I tried mine on FB for $25, no takers. If you find a buyer, tell them you have a line on another one.
Funny story about one of these when I was a kid. We lived in a 4 unit apartment and randomly we started getting billed for calls to Korea. Now the neighbor in the front unit was from Korea, which seemed odd. My mom would call the phone company and explain what was going on and they eventually said there was nothing they could do. Then I would pick up the phone and hear people talking in what I guess was Korean and I would yell to hang up. Then one day I was going to do laundry and the neighbor was in the laundry room with one of these hooked up talking to someone. My mom was very shocked that 10-11 year old me used many of George Carlin's 7 words to tell him what I thought of what he was doing.