Protocol based VLAN setup

I have several 4500 3COM switches in my LAN. These equipments where uplinked with a core gigabit switch 3COM 5500. We have about 200 IP phones D-Link DPH-150SE connected to 4500 switches and a PC behind each of these phones. These phones have a problem that when they are setted to mark a 802.1q VLAN tag, they also mark the packets originated by the PCs behind them, which must be leave untouched by the phones (untagged). This phone behaviour makes port VLAN setup not to be efective.

So, while the vendor doesn't fix this problem, i think i can setup a protocol VLAN where the 4500 switch assigns to an incoming untagged frame to a VLAN based on its protocol. SIP and RTP packets generated by phones could be, say in VLAN 2, where other packets could be in default VLAN 1. I've followed some 3COM guides, but i found no way to tell 4500 switch to recognize SIP and RTP packets. The general syntax command that refers to protocol type is:

[4500] protocol-vlan [protocol-index] {at | ip | ipx {ethernetii | llc | raw | snap } | mode {ethernetii etype etype-id | llc {dsap dsap-id | ssap ssap-id}  | snap etype etype-id}}

A usual command to recognize ip packets is:

[4500] protocol-vlan ip

We can create user-defined protocol template. For instance, if we need VLAN 100 to carry ARP for IP communication, assuming that Ethernet_II encapsulations is used, we can type this:

[4500] vlan 100
[4500-vlan100] protocol-vlan mode ethernetii etype 0806

So, i think user-defined protocol templates would be the way, but i couldn't find the exact line command (what etype match SIP and RTP ?). This is my question.