if you want a free SIP proxy, go to http://www.inin.com ( interactive intelligence ) they have a link on thier home page to download and use for free a basic copy of thier SIP proxy ( all it doesn’t do is listed in the advanced vs. basic list ). All that they need is the MAC address of the machine it will be installed on for registration. Aboslutely free! I have it and it worked for me. Installation to SIP registration of devices in 15 mins.