I've found it to be less initial setup to use DHCP option 176 for VLAN configuration, and never had a problem with any deployment using this. Any Windows server 2000 or newer support this, and the server doesn't need to be on anything but the default VLAN (and on some switches, won't work unless it is). String should include:
L2QVLAN=xx,VLANTEST=60
xx is the VLAN ID of the voice VLAN, and VLANTEST is optional but tells the phone if it can't find the designated VLAN or has problems using it to default back to VLAN 0 untagged.