In microsoft.public.windowsxp.network_web, LCBO wrote:

I suspect a line fault, or a fault in your master socket.

You need to have the phone company come out and check the line - that is the
line inside the house/apartment.  It can be quite expensive if you didn't
opt for line maintenance when setting up your phone.  Although the line may
be working fine for "analog" calls, there seems to be an issue causing the
digital portion to become disconnected when both "analog" and "digital" are
traveling down the same line.  Once, I had a similar issue living in an
apartment complex - come to find out (luckily I had the line maintenance) a
neighbor without phone service had tapped into my phone line, quite sloppily
to boot, and was causing issues with the DSL.  Bet is was causing him issues
with phones too, without any filters.