A SIP tackle/account. This is received free from providers, and you can sign-up on the web. Here are links to assist you obtain a absolutely free SIP account. Initiate a dialog for creating a call. The ask for is shipped by a consumer agent shopper to your user agent server. http://buzzgram.de/die-evolution-der-kommunikation-eine-einfuhrung-in-sip-trunking-voip-handys-softphones-und-voip-telefonanlagen/