If you’re looking for really robust, post-disaster communications, then I had a sales call the other day with a firm named Blue Force Development, http://www.blueforcedev.com. They can air drop a hummer with a bunch of communications gear into an affected area and they have less intense solutions as well. I don’t know much about them, but I was impressed.
If’ you’re looking for a less hard core solution, I’ve had experience with Twitter during the Southern California fires. Worked quite well to keep people informed (as long as they had a cell or wireless signal, of course).
My firm, NewsGator, http://www.newsgatorwidgets.com, provides a variety of widgets and RSS reader solutions that some agencies have investigated for providing updates during emergencies. Much less robust that Blue Force, but can be more mission focused than Twitter.
Hope that helps.