Caller IDwikipedia
Caller ID (caller identification, CID), also called calling line identification (CLID), Calling Line Identification (CLI), calling number delivery (CND), calling number identification (CNID), calling line identification presentation (CLIP), or call display, is a telephone service, available in analog and digital telephone systems, including VoIP, that transmits a caller's telephone number to the called party's telephone equipment when the call is being set up.
caller IDcaller line identificationCLIcalling party namecalling name and number displayCLIDcaller-identification technologyCalling numberCaller Displaydisplayed

Automatic number identification

automatic number identificationANIthe caller's number
The idea of CNID as a service for POTS subscribers originated from automatic number identification (ANI) as a part of toll free number service in the United States.
ANI is not related to newer caller ID services such as call display.

Business telephone system

PBXprivate branch exchangekey telephone system
A call placed behind a private branch exchange (PBX) has more options.

Plain old telephone service

POTSplain old telephone serviceLocal Telephone Service
The idea of CNID as a service for POTS subscribers originated from automatic number identification (ANI) as a part of toll free number service in the United States.
The services include voicemail, Caller ID, call waiting, speed dialing, conference calls (three-way calling), enhanced 911, and Centrex services.

Telcordia Technologies

BellcoreTelcordiaiconectiv
Trial results were analyzed by Bellcore members of the original team.
The company has been a major architect of the United States telecommunications system and has pioneered many services, including caller ID, call waiting, mobile number portability and toll-free telephone number (800) service.

Kazuo Hashimoto

From 1969 through 1975, Paraskevakos was issued 20 separate patents related to automatic telephone line identification, and since they significantly predated all other similar patents, they appear as prior art in later United States Patents issued to Kazuo Hashimoto and Carolyn A. Doughty.
Kazuo Hashimoto was a Japanese inventor who registered over 1,000 patents throughout the world, including patents for Caller-ID system and telephone answering machine.

Theodore Paraskevakos

In 1968, Theodore George “Ted” Paraskevakos, while working in Athens, Greece as a communications engineer for SITA, began developing a system to automatically identify a telephone caller to a call recipient.
Paraskevakos' most notable inventions relate to the transmission of electronic data through telephone lines which formed the original basis for what is now known as caller ID.

Caller ID spoofing

caller ID spoofingspoofspoofed
Legislation in the United States in made caller ID spoofing illegal for fraudulent purposes.
For example, a caller ID display might display a phone number different from that of the telephone from which the call was placed.

Nélio José Nicolai

Later in 1980 two other Brazilian inventors, João da Cunha Doya and Nélio José Nicolai, filed different patent applications for caller ID devices.
Nélio José Nicolai (c. 1940 – 11 October 2017) was a Brazilian electrotechnician who is believed to have invented caller ID.

Bell 202 modem

Bell 202Bell 202 tones
In 1995, Bellcore released another type of modulation, similar to Bell 202, in which it became possible to transmit caller ID information and even provide call-disposition options while the user was already on the telephone.
In North America, Bell 202 AFSK modulation is used to transmit Caller ID information over POTS lines in the public telephone network.

Vertical service code

vertical service codecalling featureservice feature
Most service providers however, allow the caller to block caller ID presentation through the vertical service code *67.

Voice over IP

VoIPvoice over IPvoice over Internet Protocol
Caller ID (caller identification, CID), also called calling line identification (CLID), Calling Line Identification (CLI), calling number delivery (CND), calling number identification (CNID), calling line identification presentation (CLIP), or call display, is a telephone service, available in analog and digital telephone systems, including VoIP, that transmits a caller's telephone number to the called party's telephone equipment when the call is being set up.
Voice over IP protocols and equipment provide caller ID support that is compatible with the facility provided in the public switched telephone network (PSTN).

Smartphone

smartphonesmartphonessmart phone
Smartphones can use a third-party mobile app to do the name lookup in a third-party database.
This formed the original basis for what is now known as caller ID.

Anonymity

anonymousanonymityanonymously
Similarly, some countries offer anonymous caller rejection, which rejects all calls when the subscriber's name, number (or both) is blocked.
In work settings, the three most common forms of anonymous communication are traditional suggestion boxes, written feedback, and Caller ID blocking.

Signalling System No. 7

SS7SS7 networkCCS7
A SS7 (or Signalling System 7) TCAP query may be launched by the called party's central office, in order to retrieve the information for Calling Name delivery to the caller ID equipment at the consumer's location, if the caller's name has not already been associated with the calling party's line at the originating central office.
Some of the first such services were call management related, call forwarding (busy and no answer), voice mail, call waiting, conference calling, calling name and number display, call screening, malicious caller identification, busy callback.

Toll-free telephone number

toll-free telephone numbertoll-freetoll-free number
The idea of CNID as a service for POTS subscribers originated from automatic number identification (ANI) as a part of toll free number service in the United States.
Toll free numbers usually capture the telephone number of the caller for billing purposes through automatic number identification, which is independent of caller ID data and functions even if caller ID is blocked.

Qwest Corporation

U S WEST CommunicationsMountain States Telephone & Telegraph CompanyQwest
US West Communications (now CenturyLink) was the third local telephone company to offer caller ID service in 1989.
U S WEST Communications was the first local telephone company to offer Caller ID service in 1991, nearly four years before any other local telco could do so. They were the first US telco to upgrade their PSTN to electronic switching before 1990 and they were the first to offer residential and business ISDN and later, DSL services to their customers by 1997.

Analog Display Services Interface

ADSI
This service became known in some markets as call waiting ID, or (when it was combined with call-disposition options), Call Waiting Deluxe; it is technically referred to as Analog Display Services Interface.
The service is marketed at telephone customers who subscribe to the majority of Custom Local Area Signaling Services (CLASS)-based services offered by their local telephone company (such as caller ID, Call Return, etc.) by the customization of a telephone capable of providing one-touch access to these features.

ITU V.23

V.23V23
Instead of Bell 202, the European alternative V.23 is sometimes used, (without the 75-baud reverse channel) or the data is sent using DTMF signalling.
In some European countries, (and perhaps elsewhere), V.23 Mode 2 AFSK modulation, (without the backward channel) is used to transmit Caller ID information over POTS lines in the public telephone network.

Dual-tone multi-frequency signaling

DTMFtouch-tonetouch tone
Instead of Bell 202, the European alternative V.23 is sometimes used, (without the 75-baud reverse channel) or the data is sent using DTMF signalling.
This led to the addition of the number sign octothorpe asterisk or "star" keys as well as a group of keys for menu selection: A, B, C and D. In the end, the lettered keys were dropped from most phones, and it was many years before the two symbol keys became widely used for vertical service codes such as *67 in the United States of America and Canada to suppress caller ID.

Frequency-shift keying

FSKfrequency-shift keyingfrequency shift keying
Even today, North American caller ID uses 1200 baud AFSK in the form of the Bell 202 standard.

North American Numbering Plan

Area codeArea codes<span style="white-space:nowrap;">Area code(s)
In North America and some other regions, the code is *67 (1167 rotary dial), while in the United Kingdom and Ireland, it is 141.

Direct inward dial

direct inward dialingdirect inward dialdirect inbound dialing
The caller line identification (CLI) or caller-id of extensions for outgoing calls is often set to the extension DID number, but may be the organization's central switch board number.

Truecaller

Truecaller is a mobile app that finds contact details globally given a name or telephone number, and has an integrated caller ID service to achieve call-blocking functionality and social media integration to keep the phonebook up-to-date with pictures and birthdays.

Location-based routing

location-based routing
Location-based routing is a system of rules to varying degrees of complexity dictating where inbound telephone calls from various locations are routed to. The location of call origin is normally determined by the outgoing caller ID of the caller but can also be determined by GPS position or signal triangulation, the latter being particularly useful for calls coming from mobile phones.

Prank call

prank callprank callsprank phone calls
Prank callers can now be easily found through Caller ID, so it is often asserted that since the 1990s, prank calls have been harder to accomplish and thus waning in popularity.