In the past I have used lldp to advertise the voice VLAN tag to my Cisco devices. That works! But it does seem to result in a ton of additional lines in my configuration.
I noticed that with Summit firmware 21.x and up, I should be able to use CDP, like this ...
configure cdp voip-vlan "DowntownV" ports all
Also - I noticed if I do a "show config" there is nothing in there about cdp. As if the switch is pretending to apply the command but then ignoring it.
* Slot-1 Stack.4 # sh conf | incl cdp
* Slot-1 Stack.5 #
I am running firmware: 22.214.171.124 patch1-2