You can't do 56K over a strictly analog phone
line--
Um, POTS phone lines *are* strictly analog, from the modem to the CO.
I wouldn't want to bet that 56K is impossible even with POTS copper at
each end, with suitably smart probing of the signal path and adaption
to its observed characteristics. (Which is not to say that modern 56K
modems can do that.)
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