With IPHost Network Monitor you can run simple snmp requests against a Cisco device in your network.
ciscoUnityLicUMSubscribersMax
cisco Unity Lic UM Subscribers Max
1.3.6.1.4.1.9.9.385.1.2.11
The maximum number of subscribers licensed for unified messaging.
Back to CISCO-UNITY-MIB MIB page.
IPHost Network monitor allows you to monitor ciscoUnityLicUMSubscribersMax 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.