That's slightly different. analog phone lines suffer from 'line echo', which is an echo generated by the phone line itself - because the same pair of wires is

That's slightly different. analog phone lines suffer from 'line echo', which is an echo generated by the phone line itself - because the same pair of wires is used for signals traveling in both directions. If you're thinking of the 'hybrid' , which connects the phone line to the speaker and mic, that matches the impedence of each of the three pairs of wire (to the mic, speaker, and phone line) to avoid generating echo in the first place. But they weren't perfect (and echo could be generated at other points in the line) so later, digital electronics was used to do first "echo suppression" (just zero any signal below certain magnitude) and then echo cancellation, which is very similar to acoustic echo cancellation (an AEC can probably do anything an LEC can do, but the LEC is less capable). I'm not aware of anyone doing echo cancellation using an analog circuit, but that doesn't mean no-one did. I guess it's theoretically possible but I don't see how the adaption could work.