HOWTO build a home phone-exchange

Phil sez, "I sent my Dad your HOWTO on building an intercom with an old telephone because it reminded me of something he built when I was a kid. He said: 'Mine was much posher! I made a miniature telephone exchange so that you could dial a specific extension which would then "ring", just like a "real" phone. To cap it all I had antique phones which looked good. The design was from February 1972 Practical Wireless.'" Link (Thanks, Phil!)