SNIP
Rather than use a plug-in filter, I would use a Clarity modified filtered
faceplate in the master socket, as described at Clarity Modified Master
Faceplate You can then hardwire a digital extension into the back of
that,
along with your normal telephone extension wiring.
http://www.clarity.it/telecoms/adsl_faceplate_mod.htm


I saw this a while ago and thought it was a good idea. I had a normal BT
supplied ADSL faceplate and I got thinking about if it was possible to
modify it. Turned out really easy, I popped the blastic back off then
soldered a PCB terminal block thing in place. The holes and connections were
already there so it was an easy job. Then I had to make a cutout in the
plastic.