So, if it's authenticity you want, you'll have to incorporate some sort
of noise generator on the lines. Telco quality is much better today
than 40 years ago (although you may not think so). I recall that
calling Sunnyvale from Los Gatos (or vice-versa) was a real adventure in
connectivity. Los Gatos was GTE; Sunnyvale was AT&T. I think that
someone once told me that the network interconnect was acoustic (I don't
know if that was true). But you might as well have been calling
Boston, for the line quality.
--Chuck