A rotary dial telephone, c.1940s
Modern telephones use push buttons

A telephone, or phone, is a telecommunications device that permits two or more users to conduct a conversation when they are too far apart to be heard directly. A telephone converts sound, typically and most efficiently the human voice, into electronic signals that are transmitted via cables and other communication channels to another telephone which reproduces the sound to the receiving user.

In 1876, Scottish emigrant Alexander Graham Bell was the first to be granted a United States patent for a device that produced clearly intelligible replication of the human voice. This instrument was further developed by many others. The telephone was the first device in history that enabled people to talk directly with each other across large distances. Telephones rapidly became indispensable to businesses, government, and households, and are today some of the most widely used small appliances.

The essential elements of a telephone are a microphone (transmitter) to speak into and an earphone (receiver) which reproduces the voice in a distant location. In addition, most telephones contain a ringer which produces a sound to announce an incoming telephone call, and a dial or keypad used to enter a telephone number when initiating a call to another telephone. Until approximately the 1970s most telephones used a rotary dial, which was superseded by the modern DTMF push-button dial, first introduced to the public by AT&T in 1963. [1] The receiver and transmitter are usually built into a handset which is held up to the ear and mouth during conversation. The dial may be located either on the handset, or on a base unit to which the handset is connected. The transmitter converts the sound waves to electrical signals which are sent through a telephone network to the receiving telephone which converts the signals into audible sound in the receiver, or sometimes a loudspeaker. Telephones are duplex devices, meaning they permit transmission in both directions simultaneously.

The first telephones were directly connected to each other from one customer's office or residence to another customer's location. Being impractical beyond just a few customers, these systems were quickly replaced by manually operated centrally located switchboards. This gave rise to landline telephone service in which each telephone is connected by a pair of dedicated wires to a local central office switching system, which developed into fully automated systems starting in the early 1900s. For greater mobility, various radio systems were developed for transmission between mobile stations on ships and automobiles in the middle 20th century. Hand-held mobile phones were introduced for personal service starting in 1973. By the late 1970s several mobile telephone networks operated around the world. In 1983, the Advanced Mobile Phone System (AMPS) was launched, offering a standardized technology providing portability for users far beyond the personal residence or office. These analog cellular system evolved into digital networks with better security, greater capacity, better regional coverage, and lower cost. Today, the worldwide public switched telephone network, with its hierarchical system of many switching centers, can connect any telephone on the network with any other. With the standardized international numbering system, E.164, each telephone line has an identifying telephone number, that may be called from any other, authorized telephone on the network.

Although originally designed for simple voice communications, convergence has enabled most modern cell phones to have many additional capabilities. They may be able to record spoken messages, send and receive text messages, take and display photographs or video, play music or games, surf the Internet, do road navigation or immerse the user in virtual reality. Since 1999, the trend for mobile phones is smartphones that integrate all mobile communication and computing needs.

Basic principles

Schematic of a landline telephone installation.

A traditional landline telephone system, also known as plain old telephone service (POTS), commonly carries both control and audio signals on the same twisted pair (C in diagram) of insulated wires, the telephone line. The control and signaling equipment consists of three components, the ringer, the hookswitch, and a dial. The ringer, or beeper, light or other device (A7), alerts the user to incoming calls. The hookswitch signals to the central office that the user has picked up the handset to either answer a call or initiate a call. A dial, if present, is used by the subscriber to transmit a telephone number to the central office when initiating a call. Until the 1960s dials used almost exclusively the rotary technology, which was replaced by dual-tone multi-frequency signaling (DTMF) with pushbutton telephones (A4).

A major expense of wire-line telephone service is the outside wire plant. Telephones transmit both the incoming and outgoing speech signals on a single pair of wires. A twisted pair line rejects electromagnetic interference (EMI) and crosstalk better than a single wire or an untwisted pair. The strong outgoing speech signal from the microphone (transmitter) does not overpower the weaker incoming speaker (receiver) signal with sidetone because a hybrid coil (A3) and other components compensate the imbalance. The junction box (B) arrests lightning (B2) and adjusts the line's resistance (B1) to maximize the signal power for the line length. Telephones have similar adjustments for inside line lengths (A8). The line voltages are negative compared to earth, to reduce galvanic corrosion. Negative voltage attracts positive metal ions toward the wires.

Other Languages
Afrikaans: Telefoon
Alemannisch: Telefon
አማርኛ: ስልክ
Ænglisc: Feorrspreca
العربية: هاتف
aragonés: Telefón
ܐܪܡܝܐ: ܙܥܘܩܐ
armãneashti: Telefonu
asturianu: Teléfonu
Avañe'ẽ: Pumbyry
azərbaycanca: Telefon
تۆرکجه: تلفون
বাংলা: টেলিফোন
Bân-lâm-gú: Tiān-ōe
башҡортса: Телефон
беларуская: Тэлефон
беларуская (тарашкевіца)‎: Тэлефон
भोजपुरी: टेलीफोन
български: Телефон
bosanski: Telefon
brezhoneg: Pellgomz
català: Telèfon
Чӑвашла: Телефон
čeština: Telefon
chiShona: Runhare
Cymraeg: Ffôn
dansk: Telefon
Deitsch: Foohn
Deutsch: Telefon
eesti: Telefon
Ελληνικά: Τηλέφωνο
español: Teléfono
Esperanto: Telefono
euskara: Telefono
فارسی: تلفن
français: Téléphone
Frysk: Telefoan
Gaeilge: Guthán
Gaelg: Çhellvane
Gàidhlig: Fòn
galego: Teléfono
贛語: 電話
한국어: 전화
Հայերեն: Հեռախոս
हिन्दी: दूरभाष
hrvatski: Telefon
Bahasa Indonesia: Telepon
interlingua: Telephono
Interlingue: Telefon
Iñupiak: Uqautitaun
íslenska: Sími
italiano: Telefono
עברית: טלפון
Basa Jawa: Tilpun
kalaallisut: Oqarasuaat
ಕನ್ನಡ: ದೂರವಾಣಿ
къарачай-малкъар: Телефон
ქართული: ტელეფონი
कॉशुर / کٲشُر: ٹیلِفون
қазақша: Телефон
Kiswahili: Simu
Kreyòl ayisyen: Telefòn
Kurdî: Telefon
Ladino: Telefon
Latina: Telephonum
latviešu: Telefons
Lëtzebuergesch: Telefon
lietuvių: Telefonas
Limburgs: Tillefoean
lingála: Ebengeli
Livvinkarjala: Telefon
la .lojban.: fonxa
македонски: Телефон
Malagasy: Telefaonina
മലയാളം: ടെലിഫോൺ
मराठी: दूरध्वनी
მარგალური: ტელეფონი
مصرى: تليفون
Bahasa Melayu: Telefon
Mìng-dĕ̤ng-ngṳ̄: Diêng-uâ
မြန်မာဘာသာ: တယ်လီဖုန်း
Nāhuatl: Huehcacaquiztli
Nederlands: Telefoontoestel
Nedersaksies: Tillefoon
नेपाली: टेलिफोन
日本語: 電話機
Napulitano: Telèfene
нохчийн: Телефон
norsk: Telefon
norsk nynorsk: Telefon
occitan: Telefòn
oʻzbekcha/ўзбекча: Telefon
ਪੰਜਾਬੀ: ਟੈਲੀਫ਼ੋਨ
Pälzisch: Telefon
پنجابی: ٹیلی فون
پښتو: غږلېږدی
Patois: Telifuon
ភាសាខ្មែរ: ទូរស័ព្ទ
Piemontèis: Teléfon
polski: Telefon
português: Telefone
Ripoarisch: Tellefoon
română: Telefon
Runa Simi: Karu rimay
русиньскый: Телефон
русский: Телефон
саха тыла: Төлөппүөн
Gagana Samoa: Telefoni
संस्कृतम्: दूरवाणी
Scots: Telephone
shqip: Telefoni
sicilianu: Telèfunu
සිංහල: දුරකථනය
Simple English: Telephone
slovenčina: Telefón
slovenščina: Telefon
Soomaaliga: Taleefoon
کوردی: تەلەفۆن
српски / srpski: Телефон
srpskohrvatski / српскохрватски: Telefon
Basa Sunda: Telepon
suomi: Puhelin
svenska: Telefon
Tagalog: Telepono
தமிழ்: தொலைபேசி
татарча/tatarça: Телефон
తెలుగు: టెలీఫోను
тоҷикӣ: Телефон
Tsetsêhestâhese: Aseéestsestôtse
Türkçe: Telefon
Thuɔŋjäŋ: Cɔ̈tmec
українська: Телефон
اردو: فون
vepsän kel’: Telefon
Tiếng Việt: Điện thoại
Võro: Telehvon
walon: Telefone
文言: 電話
Winaray: Telepono
吴语: 电话
ייִדיש: טעלעפאן
粵語: 電話
Zazaki: Têlefon
žemaitėška: Tilipuons
中文: 电话