Not an authoritative source, but (as a point of interest) analog landlines seem to be specified as 24 dB SNR and 300-3000 Hz passband [1], giving ~21.5 kbps information rate [2].

[1] https://www.tschmidt.com/writings/POTS_Modem_Impairments.htm

[2] https://en.wikipedia.org/wiki/Shannon%E2%80%93Hartley_theore...