Many "Winmodems" in the 90's and beyond were little more than soundcards connected to an RJ-11. Modulation/demodualtion was done in software, and this was in t

Many "Winmodems" in the 90's and beyond were little more than soundcards connected to an RJ-11. Modulation/demodualtion was done in software, and this was in the sub-1GHz days of PCs. So this was actually not uncommon, but of course binary only. There were some Linux projects to do this in a generic way - basically generate the required tones over the audio output and interpret tones over an audio input - and implement the various ITU V-series standards (though some of them were patented and could not be implemented, like V.92 for 56k). There's another one other than iaxmodem (https://stackoverflow.com/questions/3069945/open-source-soft-modem-that-runs-on-linux https://stackoverflow.com/questions/3069945/open-source-soft...) but I can't remember what it is.