My Phone Rings and The Internet Drops Its Connection

SYMPTOM
Day 1: You hear slight high pitched sounds on the phone at first, along with some mild fuzz.
Day 2: When you're talking, people ask you to speak up and you sort of get the feeling that your words are getting cut out.
Day 3: When someone calls you, your Internet connection goes down 50% of the time. When they don't call you, even though you get on the Internet, you find your Internet speed goes down remarkably.
Day 4: When someone calls you, your Internet connection always goes down.
Day 5: You can't seem to connect to the Internet without multiple attempts. You also find that if you turn off your DSL modem, the symptoms you saw on days 1 and 2 go away.

PROBLEM IDENTIFIED
Your copper wire cable may look like it's connected on the screws in your demarcation point outside your house, but in fact it may have built up moisture, corrosion, or is a wire that's about to break. Note also that copper wire is brittle in cold weather, so if there's improper insulation on the wire and in the demarcation box against cold air, it's bound to break.

RESOLUTION
Open that demarcation box, unscrew the wires carefully, and put them back on the screws again. Then, ensure the box is sealed good such that cold air cannot get in there again.

You'll find that your Internet speed goes back up, the high pitched sounds and cutouts no longer occur, and the phoneline works while you're on the Internet at the same time.