Call Waiting disconnect

I would like my Internet connection to disconnect if I recieve a call.
I have call waiting.
My OS is XP.
My modem is an Intel V.92 HAM

I add the string "+PCW=1" under Control panel-> Phone & Modem -> Modems -> Advanced -> Extra initialization commands:

My modem never disconnects when calls try to come in. Any suggestions.

I can get a GPS switch (http://www.cpscom.com/gprod/cwa.htm ) to recongnize call waiting. What do I need to do to get the modem to recognize call waiting signals? Neither PC, both with V.92 modems, disconnect when calls come in without the External GPS switch. I now have a second PC and I rather not buy another GPS switch.

Thanks in advance, JJC