High Quality Content by WIKIPEDIA articles! Caller ID (caller identification, CID), also called calling line identification (CLID) or calling number identification (CNID) or Calling Line Identification Presentation (CLIP), is a telephone service, available in analog and digital phone systems and most Voice over Internet Protocol (VoIP) applications, that transmits a caller`s number to the called party`s telephone equipment during the ringing signal, or when the call is being set up but before the call is answered. Where available, caller ID can also provide a name associated with the calling telephone number. The information made available to the called party may be displayed on a telephone`s display or on a separately attached device.