The Call button is labeled the "Primary Control Button" in the picture because it has several different functions, depending on what you are doing. When you first start the LIVE software, it is the Call button, and you can use it for making an outgoing call. When there is an incoming call, it changes to the Answer button, and you click it to answer the incoming call. During a call, the button changes to the End button, and you click it to terminate the current active call.