If you want to do the wiring yourself, I would highly recommend this
approach:

1. From the telephone company demarcation point, run a Cat 3 or Cat 5 cable
to the DSL modem. Use one pair in the cable to complete the DSL connection.
The nicely twisted computer cable should be much better at preventing
egress/ingress of unwanted signals than the conventional red/green untwisted
house wire.

2. At the demarcation point, install the filter that separates the baseband
phone signal, and connect the rest of the household phone wiring to the
output of the filter.

John Andrews, W1TAG