The Grandstream UCM6102, UCM6104, UCM6108 and UC6116 IP PBX is typically connected to the Strategic Voice Solutions system with a SIP Trunk. In a scenario where you are able to register the UCM to SVS, but when you make inbound or outbound calls it fails istypically the FROM HEADER is not set to the Strategic Voice Solutions domain URL, but an IP address where it fail authetication.  Both the TO and FROM HEADER trunk settings in the grandstream must be set to the DOMAIN URL (not IP address).  Typically something like   trk1@Packetvoice.us