Telephone

In a traditional telephone, a microphone responds to speech and produces a corresponding electrical signal. A transmission path carries that signal to another telephone, whose receiver converts it into sound. Modern systems may encode voice digitally and carry it over wired or wireless networks. A telephone network therefore involves more than the handset: it also requires transmission links and equipment that directs a call to its destination.

The telephone developed from a wider nineteenth-century effort to send sound through electrical circuits. Earlier inventors described or demonstrated devices intended to transmit speech, including Philipp Reis, whose 1861 apparatus transmitted sound but whose ability to carry intelligible speech remains uncertain. In the 1870s, Alexander Graham Bell and Elisha Gray pursued related work, initially connected to improving the telegraph. Their parallel efforts are one reason the telephone's invention cannot be reduced to a simple story of a single isolated insight.

Alexander Graham Bell received U.S. Patent No. 174,465, titled ‘Improvement in Telegraphy’, on 7 March 1876. On 10 March, Bell and his assistant Thomas Watson made an intelligible telephone communication in Bell's laboratory. Bell is conventionally credited with securing the first patent for a successful speech-transmission system and developing it into a working device. Other inventors, including Gray and Antonio Meucci, also contributed to the history of telephony; the Library of Congress notes that Bell's work built on a broader field of experimentation and that credit has been debated.

A pair of telephones could connect directly, but public service depended on joining many subscribers. Early exchanges used operators and switchboards to connect calls. Commercial instruments introduced for exchange service in the late 1870s used separate transmitter and receiver components, while a subscriber's signal alerted the operator. Automatic switching and dial telephones later let users send number signals to the exchange, which routed calls without an operator making every connection. These changes turned telephony from a point-to-point experiment into a scalable communications network.

Telephone instruments changed as engineers improved microphones, receivers, power supplies and the layout of the handset. Carbon transmitters improved the strength and clarity of early calls; later telephones combined the transmitter and receiver in one hand-held unit. Dialing also evolved from rotary pulse signaling to touch-tone keypads and electronic switching. Mobile telephony extended service beyond a fixed wire: the International Telecommunication Union's IMT-2000 standards, approved in 2000, provided an internationally agreed basis for interoperable third-generation systems carrying voice and data. Today, the word ‘telephone’ can refer both to the user device and to the broader voice-communication service, delivered through fixed, cellular or internet-based networks.