So I was thinking of the same thing the other day, and I think it's feasible. You would just need to add a custom route on your
router to use the voice bridged interface to reach 192.168.149.0/24 or something.
On those
Netlink ONT devices, you can bind a port for each WAN connection. So internet WAN connection should be bound to say LAN 1 and voice WAN connection should be bound to say LAN 2. You'd also a need a router with multiple WAN ports or configurable WAN ports like a OpenWRT device for example.
Then on your main router, the voice interface can be configured with static IP and also add a custom route for the SIP registration address. After this we ideally should be able to use any SIP application to make calls.
This of course would need the
MAC address binding to be reset, but certainly is a great idea.