it is possible that it's the Sky decoder. When I had it installed I had problems although Sky denied that it would have any effect.
At the moment the only thing that the phone connection does is send to Sky if you order pay per view movies, but note that Sky have just announced a random number of their boxes will start sending info back on viewer watching habits.
Sky have come right out and said that they feel no need to tell the lucky customers if their box will be one to send the info home to Sky... so much for privacy
Unplug the phone connection, there is nothing that Sky can do about it.