Somewhere between two-cans-and-a-string and Ma Bell lies the barbed wire fence telephone networks used by ranchers in the early 20th century. From CF Eckhardt's short history of these "rural telephone systems" at TexasHillCountry.com :
Across much of the west, to the west of old US 81 (present I-35) in Texas–and not a small part of it east of that demarcation–there was already a network of wire covering most of the country, in the form of barbed-wire fences. Some unknown genius discovered that if you hooked two Sears or Monkey Ward telephone sets to the top wire on a barbed-wire fence, you could talk between the telephones as easily as between two "town" telephones connected by slick wire through an operator's switchboard. A rural telephone system that had no operators, no bills–and no long-distance charges–was born.
Most ranch perimeter fences joined at corners, and in most cases the top wires touched each other or were even interwoven for strength. Where it became necessary for a telephone system to cross a road, all that was required was two posts about 15 feet long, buried about 3 feet into the ground for stability, and enough wire to go from one top fence wire up to the top of the post, across the road, and down the other post to the top fence wire on the other side.
More at BLDGBLOG: "Fence Phone"