Not sure of the official answer but the last outage callers heard an intercept message "Your call can not be completed as dialed. Please check the number and try your call again". The time before that, -just dead air then timed out to a fast busy. It may depend on the type of outage.
There are a lot of variables here, so the message that a caller might hear would frequently be different. It really depends on who (what carrier) the call originates with. If it can't connect, then the messaging will vary based on that carrier.
