Ethernet over unused twisted pair?

[jack-rp9/bkPP+cDYtjvyW6yDsg at public.gmane.org (Jack Coats)]

Somehow I think I have heard that two DSL modem's don't speak well
together, but that could just be my ignorance.
Then again, that doesn't ring true to me.  Since the DSL modems are a
bridge usually, and at least on my old one
it had an indicator that was basically the ATM protocol traffic it saw
over the line.  To me the indicator says it is
doing something.  Just my logic says they have a filter address and
unless specifically communicated with they
won't answer to other than the control traffic.

Sorry, just my thinking 'out loud'.

So the question is, can 2 DSL modems talk over a 'dark copper pair'?
Or is it possible to make them do so?