Yahoo News:
The system will be used to notify people about approaching tornadoes, hurricanes, blizzards and other threats. When a warning is issued for a specific county, a text-like message of no more than 90 characters will pop up automatically on the screens of newer smartphones in that area — primarily Android and Windows Phone devices — causing them to sound a special tone and vibrate.
Users do not have to sign up for the service or pay for the message. And people who prefer not to get the warnings can opt out of the system.
Buchanan said iPhones are supposed to join the system in the fall, but she didn't know if that means only new iPhones, or if software upgrades will make older models capable, too. Representatives of Apple Inc., which is highly secretive about its product upgrades, did not respond to several messages seeking details.
I'm sure the Privacy Police People™ will be concerned about this (especially if the setting defaults to on), but this is one service I'm really looking forward to.