A Conference Call is a telephone call in which the calling party wishes to have more than one called party listen in to the audio portion of the call. The conference calls may be designed to allow the called party to participate during the call, or the call may be set up so that the called party merely listens into the call and cannot speak. It is often referred to as an ATC (Audio Tele-Conference). Conference calls can be designed so that the calling party calls the other participants and adds them to the call. In most cases, the participants are able call into the conference call themselves. They do so either by dialing into a "conference bridge" (a specialised type of equipment that links telephone lines), or by using a special telephone number set up for that purpose.