Computer "answers" phone

I have an Inspiron 2650 laptop that I use in my homes in IL and CO.  When in CO it "answers" the phone, whether the laptop is on or off.  That is, after a short, partial ring, the computer opens the connection.  The calling party is still on the line and if I pick up the phone, I can talk to the caller.  However, when I am away the answering machine will not work (because it can't reach four rings).  I know it is the laptop because I have isolated it from other eqiupment (fax, etc.).  It does not matter which phone jack it is connected to.  To keep it from doing this, I must disconnect it from the phone jack (which I often fail to remember to do).  Here's the most mysterious part:  it does NOT do this in IL or in any hotel/motel I may be in.

Anyone have any ideas?