Valcom VoIP products allow you to easily add Door Intercom Stations to your facility utilizing existing network infrastructure.  The VIP-172L (IP Doorphone) series is a PoE (Power over Ethernet) device that allows integration to virtually any SIP compliant telephone system.  The VIP-172L call plate mounts in a standard 2 gang electrical box.  When the call button is pressed the VIP-172L will automatically connect via IP to a SIP telephone extension or ring group.  When the call is answered the telephone station and the VIP-172L will be in a bidirectional conversation.  If the DTMF # key is presses during the conversation the integrated form C relay will activate for 2 seconds allowing for remote door unlock.