With IPHost Network Monitor you can run simple snmp requests against a Cisco device in your network.
cueActiveCalls
cue Active Calls
1.3.6.1.4.1.9.9.420.1.2.1.2
Number of calls in progress. The number of active calls is limited by cueLicensedPortsMax.
Back to CISCO-UNITY-EXPRESS-MIB MIB page.
IPHost Network monitor allows you to monitor cueActiveCalls on Cisco device via the SNMP protocol. Download IPHost Network Monitor (500 monitors for 30 days, 50 monitors free forever) to start monitoring Cisco firewalls right now.