With IPHost Network Monitor you can run simple snmp requests against a Cisco device in your network.
ciscoUnityPortsActive
cisco Unity Ports Active
1.3.6.1.4.1.9.9.385.1.2.3
The total number of ports that are currently active with calls.
Back to CISCO-UNITY-MIB MIB page.
IPHost Network monitor allows you to monitor ciscoUnityPortsActive on Cisco device via the SNMP protocol. Download IPHost Network Monitor (500 monitors for 30 days, 50 monitors free forever) to start monitoring Cisco multiplexers right now.