On the ground: SMS notices
The Brownsville airport started offering SMS notices to people when a flight is canceled or delayed. That way anyone can stay current on the status of their flight while on transit. It's the third airport in the US to do it, and more will undoubtly follow. It's just the latest of many services using SMS to keep information current to consumers.
There are various listings of SMS services, such as Google, Yahoo! and bulk services such as Clickatell. The most important kind of alert, and one that has only really emerged since 2001, is a way to use SMS to alert others in case of an emergency. There's also services that exist purely to deliver SMS alerts when a tsunami or earthquake occurs and today's announcement of RadioShack and Cingular's campaign to sign up to 1 million users to AMBER alerts. Of course, it's always best to research these things before you may need them.