[cisco-voip] CUBE: Rewriting a response from provider and sending it back to CUCM as a 503?

[Robert Kulagowski]

OK, I'm now getting a 404 response code, which is fine, but the 404
back to CUCM 7.1.5 means that the call never drops down to the next
trunk (our PRIs) for a second attempt.

The docs that I'm reading about header modification says that changing
SIP response types isn't allowed - I can't change the 404 to a 503
apparently. (I've already confirmed that a 503 will allow the call to
fall through the route group to the next trunk).