Inspired by the "can my neighbour listen to my phonecalls" question, I'd like to ask what would be required for an attacker to snoop on an ADSL connection given physical access to the wire (so, "linesman's handset" or "Beige box" style).
Obviously, someone skilled could open up Matlab and have it done in a day or two by writing their own decoder to operate from some high-speed ADC, but is there anything straightforward that a low-effort attacker could use? I'm thinking the sort of attacker that is familiar with using (say) Kali to break wireless ethernet. How difficult is it for them to get from "wires exposed" to "ppp/etc frames"? Is it attainable with particular hardware? RTL-SDR dongles don't seem to cover the lower frequencies that DSL uses, am I correct?
I'd be interested in techniques which apply to any geographic locality.