Try adding or replace a microfilter. The microfilter is used to
split internet signal from phone signals, so that they do not
'interfere with each other', as far as i can remember
A microfilter must be plugged at the wall jack like shown in the
picture below(The rectangular box on the top right is your wall
jack, and the device right below the wall jack is the
microfilter).
If you are just replacing the
microfilter, you can ignore the instructions
If you do not have a microfilter installed before, you can try
the above method, however it is recommended to note down your
current connection plans if the above connection plan doesnt
work.
This diagram is done in 2006-2007, no guarantees if it will
work, but it still works on mine