Last week I was struggling to find the switcport settings for the NEC DT700 for us to use with one cable going to the VOIP phone and PC with dual VLANS. After a couple of testing in my LAB I was able to to get the right configurations for the switchport. Below is a sample port settings in our Cisco 3750 switch for the NEC DT700.
switchport trunk encapsulation dot1q
switchport trunk allowed vlan 2,3
switchport mode trunk
auto qos voip trust
During my test I couldn't get an ip address from the DHCP server and I had to put ip helper address to each of the VLAN interfaces.
For the NEC DT700 enable VLAN and set the LAN settings to your voice VLAN and PC settings to your data VLAN. You can also enable CDP on the NEC DT700 if you like to see the devices connected to the switch using show cdp neighbor command.