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
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rotary dial, which was superseded by the modern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.
 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
take and display photographs or
video, play music or
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.