linguistic:translation, quality:corruption
Digital telephones and voice over IP

The invention of the transistor in 1947 dramatically changed the technology used in telephone systems and in the long-distance transmission networks, over the next several decades. With the development of stored program control and MOS integrated circuits for electronic switching systems, and new transmission technologies such as pulse-code modulation (PCM), telephony gradually evolved towards digital telephony, which improved the capacity, quality, and cost of the network.

Integrated Services Digital Network (ISDN) was launched in the 1980's, providing businesses and consumers with access to digital telephony services such as data, voice, video, and fax services.

The development of digital data communications methods made it possible to digitize voice and transmit it as real-time data across computer networks and the Internet, giving rise to the field of Internet Protocol (IP) telephony, also known as voice over Internet Protocol (VoIP). VoIP has proven to be a disruptive technology that is rapidly replacing traditional telephone network infrastructure.

By January 2005, up to 10% of telephone subscribers in Japan and South Korea had switched to this digital telephone service. A January 2005 Newsweek article suggested that Internet telephony may be "the next big thing." The technology has spawned a new industry comprising many VoIP companies that offer services to consumers and businesses. The reported global VoIP market in October 2021 was $85.2 billion with a projection of $102.5 billion by 2026.

IP telephony uses high-bandwidth Internet connections and specialized customer premises equipment to transmit telephone calls via the Internet, or any modern private data network. The customer equipment may be an analog telephone adapter (ATA) which translates the signals of a conventional analog telephone; an IP Phone, a dedicated standalone device; or a computer softphone application, utilizing the microphone and headset devices of a personal computer or smartphone.

While traditional analog telephones are typically powered from the central office through the telephone line, digital telephones require a local power supply. Internet-based digital service also requires special provisions to provide the service location to the emergency services when an emergency telephone number is called.