http://evangelyze.net/cs/blogs/tony/archive/2009/03/08/securing-sip-trunks.aspxSIP trunking provides organizations with a cost-effective, reliable method of connecting the internal network and telephony systems with external VoIP and traditional phone systems over the IP network. SIP tunking is quickly replacing traditional PRIenCommunityServer 2008.5 SP2 (Debug Build: 40407.4157)