Something else to bear in mind - most of these 'farmers lines' were one wire circuits - so single wire for talking, earth ground return, local talk battery at each instrument on the circuit too.

You'd get all sorts of atmospherics and other noises during even calm weather (more in storms) (squeals, howling sounds, humming sounds, etc) - figure you basically have an aerial, with an induction coil, a speaker and a mic.