You can enable voice vlan on the switches for this. In my case vlan 1 is my data vlan and vlan 99 is my voice. All my ports are set as acess ports for vlan 1 but they all have a "voice vlan enable" statement added to each port. When you have it configured on the network switch like this, the switch will look for 00-e0-bb source addresses in the frame. When it see's those, it will automatically tag those packets for vlan 99 on ingress to the port. Then you can just put the nbx on an untagged vlan 99 port and you should be gravy. As long as you have a L3 network switch to allow you to route between your vlans, you should be ok.
Otherwise you are pretty much out of luck as the 3com switch already have prioritization for 3com voice equip ...see below:
acl number 4999
rule 0 permit type 8868 ffff
rule 1 permit source 00e0-bb00-0000 ffff-ff00-0000
rule 2 permit source 0003-6b00-0000 ffff-ff00-0000
rule 3 permit source 00e0-7500-0000 ffff-ff00-0000
rule 4 permit source 00d0-1e00-0000 ffff-ff00-0000
rule 5 deny dest 0000-0000-0000 ffff-ffff-ffff
#
qos-profile default
packet-filter inbound link-group 4999 rule 5
traffic-priority inbound ip-group 3999 rule 0 cos voice
traffic-priority inbound ip-group 3999 rule 4 cos network-management
traffic-priority inbound ip-group 3999 rule 5 cos network-management
traffic-priority inbound link-group 4999 rule 0 dscp ef cos voice
traffic-priority inbound link-group 4999 rule 1 dscp ef cos voice
traffic-priority inbound link-group 4999 rule 2 dscp ef cos voice
traffic-priority inbound link-group 4999 rule 3 dscp ef cos voice
traffic-priority inbound link-group 4999 rule 4 dscp ef cos voice
Then go to the individual port to apply the qos profile:
#
interface GigabitEthernet1/0/2
stp edged-port enable
broadcast-suppression PPS 3000
priority trust
undo jumboframe enable
apply qos-profile default <----applies the qos to the port