A system of text-like Wireless Emergency Alerts, including "imminent threat" (natural disasters such as hurricanes and earthquakes), Presidential, and AMBER (missing children) alerts, are set to roll out to mobile phones soon, via participating carriers. Here are the details you need to know.

Who's in? So far AT&T, Cellcom, Cricket, Sprint Nextel, T-Mobile, U.S. Cellular, and Verizon Wireless are on board with the Wireless Emergency Alerts (WEA) service. Subscribers will not have to sign up for the alerts; they'll be enrolled automatically.

Will the alerts work on my phone? If your phone's packaging has a sticker that looks like the illustration in the upper right of this post, it will receive the alerts. Some other phones need software upgrades to receive them. To find out for sure about your particular phone, contact your carrier (see links to participating carrier websites below). WEA-enabled, for example, include several phones current in our phone Ratings, such as Verizon's Motorola Droid Razr, Razr Maxx, and the Samsung Convoy, and the T-Mobile myTouch 4G.

Do I have a choice about receiving the alerts? You can opt out of the AMBER and weather alerts but not Presidential Alerts.

How do they know which alerts to send me? The emergency alerts will be location-based, so you'll receive alert texts appropriate to your current whereabouts. GPS isn't necessary; you'll receive alerts from whichever cell-phone tower you're closest to.

Will I be charged to receive alerts? According to CTIA - The Wireless Association, you will not be charged. The alerts are similar to text messages, but "Wireless Emergency Alerts use a different kind of technology to ensure they are delivered immediately and are not subjected to potential congestion (or delays) on wireless networks," says the agency.

Wireless Emergency Alerts on Your Mobile Device [CTIA website]

AT&T: Wireless Emergency Alerts Information
Cellcom: WEA Main Page
Cricket: CMAS Press Release
Sprint Nextel: Wireless Emergency Alerts Information
T-Mobile USA: Wireless Emergency Alerts Information
U.S. Cellular: Wireless Emergency Alerts | U.S. Cellular
Verizon Wireless: Wireless Emergency Alerts Information