AT&T has begun rolling out Wireless Emergency Alerts updates for iPhone 4S and 5, so you won't be the last folks to know if the entire northern hemisphere is about to be covered in ice à la Day After Tomorrow. You'll receive a notification from the carrier when your update is ready, but only if you're using iOS 6.1 or higher. Once installed, AMBER and Emergency alerts are automatically sent to your phone unless you switch them off via Settings, but you can't disable Presidential alerts. WEA messages are always free of charge, so you don't have to worry about going over your texting limit when notified that you need to get the hell out of dodge.