New England Tel & Tel used to refer to those a "full period lines". When my father owned an auto salvage business he was hooked up to a network over other yards so they could request parts that they didn't have. It made for some interesting listening, especially when two yards would get in an argument over something. I never heard it referred to as a six wire.The 6-wire essentially is a party line telephone. To use the old NY Telephone vernacular, it's a "hoot-n-holler" line: 1 person talks, everyone listens.