Using SIP (Session Initiation Protocol) to connect with an ITSP (Internet Telephony Service Provider) from a PBX for primarily voice communications, which can benefit the end-user with lower cost calls. For companies to take full advantage of their premise IP-PBX which communicate over IP within the enterprise, they can have a SIP trunk configured to connect to a traditional PSTN network through an Internet SIP connection. The benefits can include lower monthly calling costs for long-distance as well as International.