Call Waiting lets you know when someone is trying to reach you when you're already using the phone. You'll be alerted to the incoming call when you're already on the line. Call Waiting uses a special tone to let you know that someone else is calling. Just briefly press (don't hold down) the telephone receiver button or flash button and you can answer your second caller. To return to your first caller, just press the receiver button or flash button again. You can switch between callers as often as you like. Each conversation is private and can not be heard by the other caller. You don't have to answer the incoming call.