LEE COUNTY, Fla.- People across Southwest Florida woke up to the AMBER Alert on their cell phones when Denise Hernandez was reported missing in Immokalee overnight. But not everyone got the message.

A program called the Wireless Alert System sent out the message telling people about the missing child, but it all depends on your phone model and software.

Confusion over the program, however, set off a chain of phone calls.

The Florida Department of Law Enforcement says people were calling them all day to ask about the message, but it didn't come directly from them.

FDLE sends out alerts through email, but not text. The text alerts come from a national program through FEMA, and also include presidential alerts and disaster threats.

Robert Mason owns 'The Phone Doctor' in Fort Myers. He says while people may need to get used to the new alert system, which began at the beginning of the year, he thinks it is a good thing. "I think it's really smart. No other time have we been able to contact that many people at once. For the safety of our children, I think it's very important."

You don't have to sign up for the alerts, but not everyone received them on their phones. Mason says, "the newer the phone, the more likely you'll get the alert. It definitely does get your attention. For people who weren't used to it, they were very concerned about it."

Most major phone carriers, including Verizon, Sprint and AT&T participate in the program. If you did not get the alert, contact your phone provider for information about why. You can opt out on your phone or by calling your carrier.

Officials expect all phone will be compatible by 2014.

You can also receive AMBER Alert emails through FDLE. For more information, visit www.fdle.state.fl.us.

For more information about the program, visit http://www.fcc.gov/guides/commercial-mobile-alert-system-cmas.