With IPHost Network Monitor you can run simple snmp requests against a Cisco device in your network.
ccmPhoneExtnMultiLines
Cisco Call Manager Phone Extension Multi Lines
1.3.6.1.4.1.9.9.156.1.2.5.1.3
The number of multiline appearances for each phone extension.
Back to CISCO-CCM-MIB MIB page.
IPHost Network monitor allows you to monitor ccmPhoneExtnMultiLines on Cisco device via the SNMP protocol. Download IPHost Network Monitor (500 monitors for 30 days, 50 monitors free forever) to start monitoring Cisco wireless switches right now.