For smaller organizations, Call Trees, sometimes called Phone Trees, can work. We're talking small organizations of say 100 or 200 people with 20 to 40 people to be contacted immediately for a role to play in an emergency, with the remaining staff to be contacted up to a few hours later.
Emergency Notification, Mass Communication & Crisis Management Blog
Call Trees - an interesting idea...one that's been used in various forms and fashions for years. Under the right circumstances it may even work (in small organizations that is). More often than not, expectations far outweigh the actual probability of success. In fact, in my 25 + years of Crisis Management experience I have never seen a manual ‘call tree' even come close to being effective in a real crisis situation.