The messages are government issued and will include AMBER alerts for notifying users about missing children, emergency alerts that offer weather notifications and public safety warnings, and Presidential alerts, which are messages that are sent directly from the President.
Wireless Emergency Alerts are part of the FCC's CMAS program and are mandated by law. You may turn off alerts (except for Presidential alerts) if you choose. Go to Settings >Notifications>Turn On/Off.AT&T notes that messages sent through the Wireless Emergency Alerts system will not count against its subscriber' messaging plans. Both AMBER alerts and Emergency alerts can be turned off, but Presidential alerts are mandatory.
When the software update is delivered to your phone, you will see a message that states "Carrier Settings Update: new settings required for your device have been installed". After that, your iPhone 5 or 4S will receive all Wireless Emergency Alerts by default.
iPhone 4S and 5 users operating iOS 6.1 or later have already begun receiving the update over the air, while those using an older version of iOS will need to download the update through iTunes.
Update: As noted by several tipsters, the alerts will be available for iPhone 4 users as well.