[DanBC]

http://en.m.wikipedia.org/wiki/Party_line_%28telephony%29

> Later, independent systems applied multiple ringing frequencies for fully selective ringing. (The Bell System eschewed frequency selective ringing.) The ringers in party-line phones were tuned to distinguish several different ringing signals so that only the desired party's phone would actually ring. In this arrangement the only inconvenience of a party line was occasionally finding the line in use (by hearing talking) when one picked up the phone to make a call. If one of the parties used the phone heavily, then the inconvenience for the others was more than occasional, as depicted in the 1959 comedy film Pillow Talk.

I was going to say "not that ancient!" because I remember using a shared party line but that was in the 1980s, so pretty old I guess.