The FCC has approved what will certainly be the largest Emergency SMS system in the world:

Cell phone users will get text message alerts of emergencies under a new nationwide alert system approved late Wednesday by the Federal Communications Commission, according to FCC spokesman Robert Kenny.

It seems that the system will work in a manner similar to the TV/Radio Emergency Broadcast Systems:

Under the plan, the FCC will appoint a federal agency to create the messages and pass them on to cell phone companies that choose to participate, an FCC representative said earlier. Once that agency is named, the participating cell phone providers would have 10 months to comply with the new system's requirements.

All major carriers are expected to join the program. Read more @ CNN.