Call Waiting is a feature where someone can still ring you if you are on the phone. However, rather than hearing your phone ring, you would hear a tone sound letting you know that someone is trying to call you. You can look at your CID screen to see who is trying to reach you, and you can make choices of putting the current call on hold, and answering the call waiting, or eventually send the second caller to voicemail. Call Waiting can be turned off. If off, then anyone calling your number while you are on the phone will go straight to voicemail.