There is something else too that is going the way of the dodo: tie lines. These were useful for large universities with multiple campuses, as well as businesses with more than one hub operation in distant cities.
A tie line is usually part of a PBX system and works like this: instead of getting an outside line, you dial a special code that connects you to the PBX at the distant office. There could be multiple codes, each one connecting you to a different distant location, depending on how big your organization is. You can then call any extension in that distant PBX, OR get an outside line in that distant PBX and make a local call in that area without incurring toll charges.
Of course, tie lines, too, are pricey, but in their day they were economical if your organization had a lot of voice traffic going back and forth from each office, and saved some cash making LD calls in certain areas, too.
Nowadays, cheaper LD and Voice over IP is making tie lines quite obsolete. I currently work in a large organization that has three major complexes spread out across the state, that are connected to tie lines. All three sites have CENTREX systems, and the tie lines are accessed through it. Recently, one of the three sites migrated to a completely VoIP system, which effectively "broke" the tie line (the other two sites can no longer use the tie line to call site 3, incurring toll charges while site 3 is saving TONS of money ... all of its calles are net-routed now). Ultimately, the only option appears to be that the other two sites have to upgrade as well, but technological inertia here for things as mundane as phones moves glacially slow.
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