Telephone number

phone numbertelephone numbersphone numbers
A telephone number is a sequence of digits assigned to a fixed-line telephone subscriber station connected to a telephone line or to a wireless electronic telephony device, such as a radio telephone or a mobile telephone, or to other devices for data transmission via the public switched telephone network (PSTN) or other public and private networks. A telephone number serves as an address for switching telephone calls using a system of destination code routing. Telephone numbers are entered or dialed by a calling party on the originating telephone set, which transmits the sequence of digits in the process of signaling to a telephone exchange.

North American Numbering Plan

Area codeArea codesArea code(s)
The NANP divides the territories of its members into numbering plan areas (NPAs) which are encoded numerically with a three-digit telephone number prefix, commonly called the area code. Each telephone is assigned a seven-digit telephone number unique only within its respective plan area. The telephone number consists of a three-digit central office code and a four-digit station number. The combination of an area code and the telephone number serves as a destination routing address in the public switched telephone network (PSTN). For international call routing, the NANP has been assigned the international calling code 1 by the International Telecommunications Union (ITU).

Voice over IP

VoIPvoice over Internet Protocolvoice-over-IP
Voice over Internet Protocol (VoIP), also called IP telephony, is a methodology and group of technologies for the delivery of voice communications and multimedia sessions over Internet Protocol (IP) networks, such as the Internet. The terms Internet telephony, broadband telephony, and broadband phone service specifically refer to the provisioning of communications services (voice, fax, SMS, voice-messaging) over the public Internet, rather than via the public switched telephone network (PSTN).

Telephone exchange

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Instead, the RT is connected digitally to equipment in the telephone switch. This reduces the total amount of equipment required. Switches are used in both local central offices and in long distance centers. There are two major types in the Public switched telephone network (PSTN), the Class 4 telephone switches designed for toll or switch-to-switch connections, and the Class 5 telephone switches or subscriber switches, which manage connections from subscriber telephones. Since the 1990s, hybrid Class 4/5 switching systems that serve both functions have become common. Another element of the telephone network is time and timing.

Signalling System No. 7

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Signaling System No. 7 (SS7) is a set of telephony signaling protocols developed in 1975, which is used to set up and tear down most of the world's public switched telephone network (PSTN) telephone calls. It also performs number translation, local number portability, prepaid billing, Short Message Service (SMS), and other mass market services. In North America it is often referred to as CCSS7, abbreviated for Common Channel Signaling System 7. In the United Kingdom, it is called C7 (CCITT number 7), number 7 and CCIS7 (Common Channel Interoffice Signaling 7). In Germany, it is often called ZZK-7 (Zentraler ZeichengabeKanal Nummer 7).

VoIP phone

IP PhoneIP PhonesEthernet-based phone
A VoIP phone or IP phone uses voice over IP technologies for placing and transmitting telephone calls over an IP network, such as the Internet, instead of the traditional public switched telephone network (PSTN). Digital IP-based telephone service uses control protocols such as the Session Initiation Protocol (SIP), Skinny Client Control Protocol (SCCP) or various other proprietary protocols. VoIP phones can be simple software-based softphones or purpose-built hardware devices that appear much like an ordinary telephone or a cordless phone. Traditional PSTN phones are used as VoIP phones with analog telephone adapters (ATA).

Overlay plan

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It was originally established as an area code specifically for cell phones and pagers in New York City, but soon after, the FCC said area codes going forth could not be service-specific, but they allowed 917 to remain as such. However, 917 is being used for landlines in New York City on a limited basis. List of area code overlays. Interexchange carrier. Telephone exchange. Telephone numbering plan. Exhaust date.

Toll-free telephone number

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Countries around the world use various dialing prefixes to denote toll-free services in their telephone networks. Toll-free numbers in the North American Numbering Plan (NANP) are commonly called "800 numbers" after the original area code which was used to dial them. They include the area code 800 (since January 1, 1966), 888 (since March 1, 1996), 877 (since April 4, 1998), 866 (since July 29, 2000), 855 (since October 9, 2010), 844 (since December 7, 2013), and 833 (since April 22, 2017). Area codes reserved for future expansion include 822, 880 through 887, and 889. The original Wide Area Telephone Service is obsolete.

Caller ID

caller line identificationCLIcall display
In the typical telephony environment, a PBX connects to the local service provider through Primary Rate Interface (PRI) trunks. Generally, although not absolutely, the service provider simply passes whatever calling line ID appears on those PRI access trunks transparently across the Public Switched Telephone Network (PSTN). This opens up the opportunity for the PBX administrator to program whatever number they choose in their external phone number fields. Some IP phone services (ITSPs, or Internet Telephony Service Providers) support PSTN gateway installations throughout the world. These gateways egress calls to the local calling area, thus avoiding long distance toll charges.


As of 2015, the landline telephones in most residential homes are analog—that is, the speaker's voice directly determines the signal's voltage. Although short-distance calls may be handled from end-to-end as analog signals, increasingly telephone service providers are transparently converting the signals to digital signals for transmission. The advantage of this is that digitized voice data can travel side-by-side with data from the Internet and can be perfectly reproduced in long distance communication (as opposed to analog signals that are inevitably impacted by noise). Mobile phones have had a significant impact on telephone networks.


short message servicetext messagetext messages
According to one market research report, as of 2014, the global SMS messaging business was estimated to be worth over $100 billion, accounting for almost 50 percent of all the revenue generated by mobile messaging. Adding text messaging functionality to mobile devices began in the early 1980s. The first action plan of the CEPT Group GSM was approved in December 1982, requesting that "The services and facilities offered in the public switched telephone networks and public data networks ... should be available in the mobile system." This plan included the exchange of text messages either directly between mobile stations, or transmitted via message handling systems in use at that time.

Telephone tapping

However the government can tap mobile phones with the cooperation of the phone company. It is also possible for organizations with the correct technical equipment to monitor mobile phone communications and decrypt the audio. To the mobile phones in its vicinity, a device called an "IMSI-catcher" pretends to be a legitimate base station of the mobile phone network, thus subjecting the communication between the phone and the network to a man-in-the-middle attack. This is possible because, while the mobile phone has to authenticate itself to the mobile telephone network, the network does not authenticate itself to the phone.

Vertical service code

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Local Area Signalling Services (LASS) and Custom Calling Feature Control Codes: de:Vermittlungstechnische Leistungsmerkmale (öffentliche Netze) Mobile dial code. Pat Fleet – Prompt voice for most U.S. AT&T implementations of VSC features. Public switched telephone network. Short code. Signalling System 7.

UK telephone code misconceptions

common misconceptionerroneous UK telephone codesmisquoted
Telephone numbering plan.

Wireless home phone

A wireless home phone service is a service that allows a regular wired telephone to connect to a cellular network, as if it were a mobile phone. It is an example of a wireless last mile connection to the public switched telephone network, also known as a wireless local loop. A small device, about the size of a home wireless router, contains the necessary electronics which allow plain old telephone service to be provided to one or two telephone jacks on the back of the unit, as well as having a small radio antenna and a transceiver for the wireless side of the connection. LED indicator lights on the front typically show signal strength and voicemail messages waiting.

Index of telephone-related articles

Plain old telephone service (POTS). Private branch exchange. Public switched telephone network. Satellite phone. Sidetone. Telecommunications. Telephone. Telephone call. Telephone directory. Telephone exchange. Telephone line. Telephone newspaper. Telephone number. Telephone switchboard. Telephone tapping. Telephony. Thomas Edison. Timeline of the telephone. Tip and ring (Wiring terminology). Toll-free telephone number.

Integrated Services Digital Network

ISDN is also used as a smart-network technology intended to add new services to the public switched telephone network (PSTN) by giving users direct access to end-to-end circuit-switched digital services and as a backup or failsafe circuit solution for critical use data circuits. ISDN is used heavily by the broadcast industry as a reliable way of switching low-latency, high-quality, long-distance audio circuits.


GSM (850/900/1800/1900) GSM/GPRS/EDGEGSM technology
International Mobile Subscriber Identity (IMSI). Long Term Evolution (LTE). MSISDN Mobile Subscriber ISDN Number. Nordic Mobile Telephone (NMT). ORFS. Personal communications network (PCN). RTP audio video profile. Simulation of GSM networks. Standards. Comparison of mobile phone standards. GEO-Mobile Radio Interface. GSM 02.07 - Cellphone features. GSM 03.48 – Security mechanisms for the SIM application toolkit. Intelligent Network. Parlay X. RRLP – Radio Resource Location Protocol. Um interface. Visitors Location Register (VLR). GSM Association—Official industry trade group representing GSM network operators worldwide. 3GPP—3G GSM standards development group.