High Quality Content by WIKIPEDIA articles! A VoIP phone uses voice over IP (VoIP) technologies allowing telephone calls to be made over an IP network such as the Internet instead of the ordinary PSTN system. Calls can traverse the Internet, or a private IP network such as that of a company. The phones use control protocols such as Session Initiation Protocol (SIP), Skinny Client Control Protocol (SCCP) or one of various proprietary protocols such as that used by Skype.