This sounds like a job for a custom agent that you configure to "Poll" each fax line on a schedule and then reports back to unicenter on it's status. I've written a couple of agents already and they really aren't that hard to get running, they just take some planning.
I'm not sure but it also sounds like a good candidate for the SLA option. I don't quite think that SLA would dial each line, but if you had the agent in place, SLA could watch the agent.
let me know if you want to go the route of a custom agent. I'd be willing to help out.
Martin
If the sky is blue and the Sun is yellow.... Why isn't the air Green?