You guys all read books like "The Mad Scientist's Club" when you were kids, right?
I recall that in this book they (the pre-adolescent boys in the Mad Scientists Club) devised (among many other things) an intercom system that allowed them all to communicate from house to house across a small town, using its power grid.
I know there are in-house (room to room) intercom kits that you can buy, and they work with some success, but is it possible on this scale? Not that i'd try it, mind you. I suppose there are a lot of obstacles, i.e. having to filter out a 60hz AC hum with a huge amplitude, for starters. You'd be limited to AM instead of FM, I presume, blah blah.
I realize that it is a fictional book and it has a lot of, shall we say "embellishments" for the sake of the story. For instance, they often used lots of radio equipment, and while nothing seemed to have antennas on it, nobody ever mentioned line-of-sight, signal gain, pine trees, radio control frequencies vs. ham radio frequencies, the FCC or the usual stuff, most everything had a perfect 5+ mile range. Maybe the RF situation in the sky was different in the 1960s, eh?
I had completely forgotten about this 'intercom system' i read about 20 years ago, until I overheard (yet another) discussion about the "broadband over powerlines" concept that people have been debating the last few years.
For what it's worth, I remember that book fondly in my youth, and lately I've been developing a small (but present) interest in communications using unconventional means.
-phaeton