If you subscribe to your telephone company's call waiting service and your ISP does not support V.92 nor the Modem-on-Hold feature
, then you will need to disable call waiting within your dialing software. For Dial-Up Networking, go to Start | Control Panel | Modem or Phone and Modem Options, click on Dialing Properties, and enable/check the option "To disable call waiting, dial: ____" The default setting is "*70" (without quotes).
If you subscribe to your telephone company's call waiting service and if your ISP does support V.92 as well as the Modem-on-Hold feature, you can use the Modem-on-Hold application to accept or ignore incoming calls. This application is installed along with the modem driver and can be opened via Start | Programs.