I appreciate the responses 
We always just use DHCP option 43...
Do you have a dedicated voice VLAN? The phones support LLDP-MED auto voice VLAN and you can just run the DHCP server in the Mitel... That is the easiest and recommended way these days.
Option 43 would be easiest for me to try as we already do that for MX-ONE/M400 in our lab using a Windows DHCP server. I can also use VLANs for testing... I understand that LLDP-MED is on the network switch side, right? I'll take a look at that.
*EDIT: I realized you probably mean to use the MiVB as the DHCP server with option 43...
It doesn't matter what is serving up DHCP really... If you are using VLAN's you will need two DHCP scopes/servers. Using option 43, you define it as a ASCII text or "Custom Text" option.
In the default data VLAN, you give it an option that essentially does nothing except tell the phone to move to the voice VLAN (VLAN 6 in this case, using an example address of the MiVB server at 192.168.192.10 as call and tftp server, adjust as necessary)
id:ipphone.mitel.com;sw_tftp=192.168.192.10;call_srv=192.168.192.10;vlan=6;l2p=6;dscp=56Then if you are not using the Mitel itself in the voice VLAN for DHCP, you set the DHCP server for that VLAN to NOT have a VLAN tag.
id:ipphone.mitel.com;sw_tftp=192.168.192.10;call_srv=192.168.192.10;l2p=6;dscp=56I still say the better way these days is to use LLPD-MED to "move" the phone to the voice VLAN, than only one DHCP scope is required in the voice VLAN.