I.

Introduction

Telephone, instrument that sends and receives voice messages and data. Telephones convert speech and data to electrical energy, which is sent great distances. Modern technology has made the telephone much more portable, convenient, and versatile. Lightweight, handheld cell phones make it possible to place and receive calls on-the-go in many locations and at any time. Traditional telephones now link with radio, Internet, and satellite services as part of global telecommunications.

Telephones play a vital role in business and the economy, as well as in the personal and family lives of individuals. Telephones also save lives and provide security by making it possible to summon help quickly in an emergency (as in the 911 service in the United States) and contact law enforcement or medical services. The telephone has other uses that do not involve one person talking to another. Instead, an automated menu can allow a caller to pay bills, obtain prerecorded information, or retrieve messages from an answering machine. In 2004 there were 606 main telephone lines per 1,000 people in the United States and 566 main telephone lines per 1,000 people in Canada.

About half of the information passing through telephone lines occurs entirely between special-purpose telephones, such as computers with modems. A modem converts the digital bits of a computer’s output to an audio tone, which is then converted to an electrical signal and passed over telephone lines to be decoded by a modem attached to a computer at the receiving end. Another special-purpose telephone is a facsimile machine, or fax machine, which produces a duplicate of a document at a distant point.