There are two types of SIP Phones. A hardware SIP IP phone and a software SIP phone. The first type (hardware SIP phone) looks just like a regular telephone handset but it uses the Internet Protocol (IP) to communicate the voice conversation. The software SIP phones are used as software applications on a computer. They allow therefore any computer with a speaker and microphone to behave like a telephone. You also need a broadband internet connection and a subscription service with a VoIP provider or with a SIP proxy server.