With IPHost Network Monitor you can run simple snmp requests against a Cisco device in your network.
cSipStatsGlobalDeclineIns
Cisco Sip Stats Global Decline Ins
1.3.6.1.4.1.9.9.152.1.2.6.3
This object reflects the total number of Decline (603) responses received by the user agent since system startup. Decline responses indicate that the called party's end system was contacted successfully but the called party explicitly does not wish to, or cannot, participate.
Back to CISCO-SIP-UA-MIB MIB page.
IPHost Network monitor allows you to monitor cSipStatsGlobalDeclineIns on Cisco device via the SNMP protocol. Download IPHost Network Monitor (500 monitors for 30 days, 50 monitors free forever) to start monitoring Cisco switches right now.