With IPHost Network Monitor you can run simple snmp requests against a Cisco device in your network.
cSipStatsClientForbiddenOuts
Cisco Sip Stats Client Forbidden Outs
1.3.6.1.4.1.9.9.152.1.2.4.8
This object reflects the total number of Forbidden (403) responses sent by the user agent since system startup. Outbound Forbidden responses indicate that requests received by this system are understood but this system is refusing to fulfill the requests.
Back to CISCO-SIP-UA-MIB MIB page.
IPHost Network monitor allows you to monitor cSipStatsClientForbiddenOuts on Cisco device via the SNMP protocol. Download IPHost Network Monitor (500 monitors for 30 days, 50 monitors free forever) to start monitoring Cisco mobile switches right now.