John - I've heard mention on the boards about a service call Switch Redirect...it sounds like your current CrisisLink service...
http://www.infotelsystems.com/bri_backup_to%20pri.htm In the event of a Mass Evacuation or Switch failure - Our Recovery plan consist of Sister Properties with existing switches - We have the main number setup to route to another property with Bell South and our Toll Free numbers route via Sprint....
In the event of an "isolated" evacuation (say a 1/3rd of the building)- I use Symposium Emergency Scripts and the IDC Table in conjuction with phantoms/ACD NCFW to route main departmental numbers to individuals or an alternate Emergency Ops Center...