The function allows you choosing a number that you want in order to
light up during the call to traditional telephones. You can also unlist the
number and it won’t light up.
This is a Voice over Internet Protocol (VoIP) and streaming media service based on the Session Initiation Protocol (SIP) by which Internet telephony service providers (ITSPs) deliver telephone services and unified communications to customers equipped with SIP-based private branch exchange (IP-PBX) and Unified Communications facilities