This was probably due to mechanical (Strowger, Crossbar) mechanical switches. https://en.wikipedia.org/wiki/Crossbar_switch ×

These had a very limited ability to make connections; only a small proportion of telephones on a given switch could call each other at a given time. I believe these were called "blocking switches".

These things, called "switches", often had the ability to connect to 10,000 subscriber loops.

Later, electronic telephone switches allowed more extensive connections. https://en.wikipedia.org/wiki/Electronic_switching_system ×

The big problem is, these switches might have been replaced only after decades of use.

It probably didn't take all that many long-term (modem) connections to use up a mechanical switch's connection ability.

Jim Bell

On Thursday, December 27, 2018, 4:07:24 AM PST, P.J. Westerhof <Peter@isoc.nl> wrote:

Correct.
If memory serves me right, not only because some modems caused technical
issues with installed telephone infrastructure. But also because the
then customary flat rate for local telephone use meant that you could
get on the Internet almost indefinitely if an Internet access point was
within reach, f.i. university or library.
This extra and sustained load could cause technical issues in itself,
but it also cost the phone companies a pretty penny in lost income. No
wonder the phone companies were quick to change their tariffs to usage
based.

Gr.
Peter
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Op 26-12-18 om 23:21 schreef jim bell:
> I think there was a time in the late 1970's when phone companies
> expressed resentment that their users were employing modems on their
> phone lines.