Xbox live stops working

When I sign on to Xbox Live, it works fine...however, it will disconnect everytime the phone rings.  I have tried to connect it while the phone rings and it doesn't work, but it does work when I try to connect it while someone is talking on the phone after the ringing has endend.  I have a new router so i don't feel like that is the problem.  Years ago when I tried to add cable to one more room in my house, I was told by Comcast that the cable signal fromt the street was being divided up into too many different locations in the home and the signal strenght was to low.  However, when I am logged on, the router connection is perfect.  It will disconnect at random times for no known reason, and it disconnects whenever the phone rings.