How can my IP phone or my software make and receive calls?

The IP phone, or the software connected to the Messagenet VoIP servers, uses a protocol called SIP (Session Initiation Protocol) which allows it to record the Internet address through which it is being connected to the Messagenet servers. Then the servers can forward the calls to its number. In order to do this and to identify the user associated to a specific phone, all SIP terminals must have an identification (URI) and a password, which Messagenet assigns to its subscribers.