[cisco-voip] What SIP response code does CUCM need to try another trunk?

[Robert Kulagowski]

We're looking to make our trunking more robust. We've had occasions
where we get a 404 from our provider for a call which _should_ work.
We're troubleshooting that.

The 404 makes CUCM stop processing, even if there's more than one
trunk group (I'm thinking SIP as a primary, with PRI as a secondary)

If I rewrite the 404 into something else on the SBC, will that work?
If yes, what does CUCM look for to try the next entry?