This looks like a great idea:
http://mobile.nytimes.com/article?a=786821&f=21

"cellphone users in New York and Washington will soon be able to receive alerts by text message in the event of a national or regional emergency... Text messages will be sent to customers of participating cellphone companies who are in an area affected by the emergency. "

There's an opt-out option for all but Presedential alerts, and it's a limited roll-out, but it sounds promising. I wonder if older cel phones will be able to opt-in without having to upgrade?