If you have an iOS device that uses a cellular connection, from time to time, you may need to update the carrier settings. The settings updates are small files that can include updates such as network, calling, cellular data, messaging, personal hotspot, and voicemail settings.
To check to see if your carrier settings need to be updated, tap on Settings > General > About. If an update is available, a prompt to update will appear.
If you need to know the version of the carrier setting on your device, tap Settings > General > About and look next to “Carrier.”
For AT&T customers using certain iPhones, there was a recent update that enables governmental and Amber alerts on certain iPhone devices running iOS 6.1 or later. While the software update is mandatory, you are not charged for the data to deliver it and Wireless Emergency Alerts will never count against your messaging plan. The update will be sent to users with iOS 6.1 or higher.
To learn more, you can read the Apple knowledge base article from which this was written.