If you subscribe to Call Waiting Service from your telephone company, you will want to disable it when you are dialing into the Internet. Here's how to do that in Windows XP. The process is similar on other operating systems.
1. Click the START button, move your cursor to SETTINGS, click on CONTROL PANEL
2. Double-click PHONE AND MODEM OPTIONS
3. Select MY LOCATION and click EDIT
4. Check the box before TO DISABLE CALL WAITING, DIAL; a checkmark will appear in it and the field at the far right of that line will activate. In that field select the appropriate code for disabling Call Waiting; it is usually*70 Click APPLY, then OK