Voice VLAN on an old Cisco 7600?

Hey Gang,
I've inherited an incredibly old Cisco 7609 to use as a PoE switch for our office. I've got everything working the way I want except voice VLAN which is driving me mad.

I've combed everywhere I can for instructions on how to ensure LLDP-MED is turned on but I'm not sure the switch even supports it. I've also turned on CDP as the Polycom handsets say they support that too.

What I've noticed so far is that the LLDP neighbor list seems to be in moderat flux with the phones showing up and disappearing, and some disappearing permanently until they've been rebooted.

Here's what I've tried as a relevant config.

Cisco IOS Software, c7600s72033_rp Software (c7600s72033_rp-ADVIPSERVICESK9-M), Version 15.3(3)S6, RELEASE SOFTWARE (fc1) System image file is "sup-bootdisk:c7600s72033-advipservicesk9-mz.153-3.S6.bin" ! cdp tlv-list VoIP port-id capability version platform native-vlan vvid cos power-available hello-protocol cdp filter-tlv-list VoIP ! lldp timer 20 lldp run ! interface GigabitEthernet9/48 description Default-31 switchport switchport access vlan 31 switchport mode access switchport voice vlan 4006 logging event link-status mls qos trust cos spanning-tree portfast 

!

The cdp stuff is kinda a shotgun approach just from desperation. Any ideas how to get this working?