The proverbial "yes and no".
I seriously looked at FX for my residence a couple of times within the last 10 years or so.
The install cost was medium monumental -- hundreds of dollars -- but the monthly recurring was a pittance -- under $2, as I recall. The monthly was that cheap because it wasn't very far -- this was for FX from the next exchange distant. It was a straight per-mile thing, and the 'worst case' distance was under 5 miles (I had them do numbers to three nearby COs, I knew the more distant one had the right kind of gear, wasn't sure what the others had, or how the distance stacked up.) I was looking at ISDN, and wanted features that were only available from certain kinds of switch. Unfortunately the one in 'my' C.O. did -not- support the particular features I wanted. Hence the FX investigation.
The poor telco rep -- who had apparently never heard of such a thing
-- had to do a _lot_ of digging, get a special services quote on the install costs, etc. and then was utterly _amazed_ at how low the monthly cost was. (I was, too!)
The idea of _ISDN_ FX took a lot of the engineering people somewhat by surprise, or so I heard, but it _was_ in the tariffs.
"In-state" long distance can still be obnoxiously priced. Including in-state 800 service.
I know of at least one manufacturing company -- located jut outside of a fairly _small_ town, that maintains a tie-line to the "big city" circa 50 miles away. They have a national 800 number, too. but there's enough call-volume to the city to justify the ongoing cost of the dedicated line. Probably not enough to justify *installing* it, if they had to do it today, but enough to _keep_ it, since the install is a 'sunk cost' -- long sunk, probably 50 years, now.
I *really* confused their switchboard one day, when I called "out of the blue" to request a quote on an order. I was calling from two states away, and the call came in on their city tie-line, *not* their800 number. For which there was a _simple_ explanation, I had family in the city, had called _them_ to get a referral, _and_ the phone number. Oddly enough, the 800 number was _not_ listed in the local phone book _there_. Since my then place-of-work had flat-rate (unmetered) _outgoing_ Long Distance, I didn't bother to check for any other numbers.
After I got a salesman, that conversation got sort-of funny. He was reluctant to quote on the order -- stated that he 'almost surely' would not be competitive, "particularly with the cost of shipping figured in", with suppliers around Chicago, where I was. As it turned out, _including_ shipping, his price was almost 1/3 *under* the best price I got locally. My order was comparatively small for a manufacturer, low 4 figures. But, as it turned out, they got a *LOT* of other business from the Chicago area as a result of my purchase -- some _big_ users heard about the pricing I got, and were placing rail-car size orders. For several years they even had a sales office here.
Remote forwarding is relatively *expensive* -- you pay a 'message units' charge for every call. Depending on what the monthly is for for the FX pair, it can be a _lot_ cheaper.
Making a WAG about the monthly for an across-town like that FX, The break-even point could easily be only 6-8 calls a day.
"Keeping" it can be relatively inexpensive. Putting it in, in the first place was where the big expense was.