Wireless Emergency Alerts (WEA), also known as CMAS, is a part of a national alerting system called IPAWS (Integrated Public Alert and Warning System) that enables emergency management officials to rapidly disseminate the warnings and safety information via text alerts to wireless phones based on the phones’ geographic location.
WEA messages are free. They are a public service brought to you by Sprint in cooperation with Federal, State, and local public safety agencies.
Check out these links for more information including if your phone is capable, how to turn it on and off and a list of markets which have this functionality rolled out. Expect more markets to come online soon.