I used to have a lot of line noise problems with my 1200 baud modem.
What was sudgested to me was to put a toriod transformer on the line.
This is easily done by getting a large toroid core from your local
electronics shop, a toroid core is a ceramic/metal "donut", and wind the
telephone line in through the center of the core and out around the
ouTside five or six times. This is a easy and cheap fix that does not
have the hassels of having to use sofware to fix a hardware problem.