With IPHost Network Monitor you can run simple snmp requests against a D-Link device in your network.
swVoiceVlanDeviceActiveTime
Switch Voice Vlan Device Active Time
1.3.6.1.4.1.171.12.74.2.3.1.4
The active time of the voice device.
Back to VOICE-VLAN-MIB MIB page.
IPHost Network monitor allows you to monitor swVoiceVlanDeviceActiveTime on D-Link device via the SNMP protocol. Download IPHost Network Monitor (500 monitors for 30 days, 50 monitors free forever) to start monitoring D-Link switches right now.