Open WRT capabilities

To lay some groundwork, I have an SPA 192 that we're using for streaming audio services (music on hold) however due to a bug in the SPA192 it refuses to negotiate SENDONLY audio which means i must use a conference bridge style call to establish the music on hold with inbound callers.

This is obviously not ideal as I don't want my customers talking with each other on hold.

I already have a firewall in place, a watchguard firebox that nobody can seem to figure out how to make work the way we want it to.

What I want to do is some sort of packet inspection and block all inbound UDP RTP traffic from my vendor's SBC, BUT ONLY to the SPA192. Is this doable on OpenWRT?

why not auto-mute the customers?

you know the ip address and the RTP UDP range on your end, right? so you can create a deny rule.

No chance of a fix from Cisco, I presume?