VoIP telephone
Voice over Internet Protocol, or VoIP, telephone products connect to VoIP, or Internet telephony, systems, which use packet-switched telephony to transmit calls over the Internet as opposed to the circuit-switched telephony used by the traditional Public Switched Telephone Network (PSTN).
VoIP telephones look and largely function like standard phones, but they have built-in IP technology and an RJ-45 Ethernet connector instead of the standard RJ-11 phone connector that enables the VoIP phone to connect directly to a router for making and receiving IP calls. A standard phone can also function as a VoIP telephone when used with an analog-to-digital converter called an ATA, or analog telephone adaptor. Another option is to bypass the phone entirely and simply use a VoIP-capable computer to make and receive IP calls.
See "The Difference Between VoIP and PSTN Systems" in the Did You Know... section of Webopedia.
Also see the VoIP Meets WiFi article in the Did You Know? section of Webopedia.


