In telecommunication, telephony (pronounced /təˈlɛfəni/ or teh-LEH-fuh-nee) encompasses the general use of equipment to provide voice communication over distances, specifically by connecting telephones to each other.
IP Telephony is a modern form of telephony which uses the TCP/IP protocol popularized by the internet to transmit digitized voice data. Contrast this with the operation of POTS (an acronym for "Plain Old Telephone Service").
Digital telephony is the use of digital technology in the provision of telephone services and systems. Almost all telephone calls are provided this way, but sometimes the term is restricted to cases in which the last mile is digital, or where the conversion between digital and analog signals takes place inside the telephone. Telephony was digitized to cut the cost and improve the quality of voice services, but digital telephony was then found useful for new network services (ISDN) to transfer data speedily over telephone lines.