Are you using a pay as you go mobile? Under that definition, everyone that 'tops up' is connected.
Recently I got a pair and they did help: http://imgur.com/a/03Ipl , but as always this is what that companies FAQ says about the process:
WHAT: ----- Wireless Emergency Alerts (WEAs) are free wireless notifications that are delivered to your mobile device as part of a new public safety system provided by Authorized Senders. They are designed to inform you of imminent threats to safety or missing persons alerts in your area.
In order to receive WEAs, you must have a capable device and be located in an area (e.g., county) targeted by Authorized Senders to receive the alert.
If every provider has some sort of program like this that connects everyone on that network.