This stand-alone 4 Port FXS SIP Version 4 Analog provides superior voice-technology for connecting legacy telephony and PBX systems as well as integration with new IP-Based PBX architecture. This product is well suited for VoIP deployments and is designed to be fully interoperable with leading SoftSwitches, Gatekeepers, and SIP servers. Please order careful and inspect upon receipt because there are no returns accepted.Thank you...