VoIP Definition: Voice over IP (also called VoIP, IP Telephony, and Internet Telephony) refers to the set of technologies that enable the routing of voice communications over the Internet or a computer network. To place calls via VoIP, a user will need a software based sip phone program OR a hardware based VoIP phone. Phone calls can be made to anywhere and to anyone: Both to VoIP numbers as well as PSTN phone numbers.