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.
I would guess WATS and long distance packages has made most FX lines obsolete. There was toll free before 800 numbers but it was manual and a local number added a comfort factor. Obviously today a business's 800 number is more convenient for anyone. Further, businesses have outward long distance packages so the cost of paying for an FX trunk (that only worked in a specific city) couldn't be justified.
But there is another type of "FX" service that seems not to have gone away even though the need has. Philadelphia has a local city zone and message units for more distant suburban calls. Many suburban businesses had a city phone number for the same reason companies had FX lines. Even some suburban homeowners who made a lot of city calls had a second line with a city number. AFAIK, many suburban businesses still maintain their existing city phone numbers even though today the need isn't as much.
(The following is the economic analyis for those interested).
The message unit charge has been 7c for at least the last 40 years. Now 7c 40 years ago was like 50c today and say a monthly usage of 100 units comes to some serious money in today's terms (equivalent of $50) while today it's $7 which isn't a big deal. Further, Verizon has increased local calling area sizes and reduced zone charges. My guess is today it probably costs a business far more to maintain the city line than whatever they save in message units, and customers don't give making a suburban call a second thought today.
In looking through the yellow pages I noticed many businesses had multiple numbers. However, for some time Verizon offers remote forwarding -- that is you get a local number but it really isn't a line -- it just forwards calls to your actual number. That's more to imply a business has a local presence than to save customers toll charges.
I guess that businesses maintaining a distant line never gave it any thought and just pay for it month after month. A few businesses had Enterprise service they kept as well until that was finally discontinued a few years ago (at least such numbers are gone from the city phone books).
My own employer used tie lines in distant places to save on toll charges 25 years ago. But now they have more modern bulk purchase toll service arrangements, all done automatically. We once dialed various codes, but now just dial 9+ for all outside calls.