In another thread Pat mentioned FX lines. As mentioned, these were
> used to save on long distance changes -- customers would make a local
> call to a distant business and the business could call its customers
> for the cost of a local call. This service was not cheap.
> At a resort I visited that had FX lines to a city 75 miles away, the
> switchboard had special heavy cord pairs. Extensions authorized for
> FX had a second jack underneath in which the heavy cord was inserted.
> I heard FX lines used higher voltage thus the heavy cords. I don't
> know what kind of special wiring, if any, was in the telephone sets.
That does not sound like POTs FX service; rather some kind of tie line set up.
True FX service is a nailed interoffice trunk between your c.o. and the distant c.o. The line side of the service; i.e. from your c.o. to your premises, is no different than any local loop and requires no special equipment on your premises.
Then, there is "phantom" FX service, still in use in the Los Angeles metro area (and perhaps other areas where SBC rates a particular office code (prefix) as being in downtown LA when, in fact, it is in a c.o. in a nearby town that would otherwise be a toll call to downtown LA. That is simply a billing accounting exercise.