[aftbit]

>Anecdotally, fence phones were still being used throughout the 1970s and perhaps even later. C.F. Eckhardt describes calling his parents who lived in rural Texas and still used a fence phone; their number was simply 37, designated on the small local network by three long rings and one short ring.

Is this perhaps an OCR or typography error? If the number were "31" that would make much more sense to encode as three long one short. A stylized 1 can look a bit like a 7 depending on how the characters are drawn.

[pseudohadamard]

We still run comms over steel wire today, only most of the time we don't know it, it's called CCS and makes for really cheap "copper" wire. For example a neighbour bought a roll of remarkably cheap Cat5 a few months back and, yeah, I don't think your ethernet cable should have a magnet able to stick to it.