This is a device allowing a user to make VoIP calls using session initiation protocol (SIP). SIP is a telecommunication technology developed as a fast, easy standard for delivering IP-based data, voice, and video communications.
A message which is played to the called party before answering the call, in the most cases the message tells who is calling, the name or telephone number helping you to decide how to answer to the call and sometimes whether to answer it at all.