WASHINGTON (CNN) -- A nationwide alert system will use cell phones or other mobile devices to send text messages to Americans when an emergency occurs, the Federal Communications Commission will announce Wednesday, according to an FCC representative.

The representative said cell phone companies that voluntarily opt into the system would send text-based alert messages to subscribers in response to three types of events:

- A disaster that could jeopardize the health and safety of Americans, such as a terrorist attack; these would trigger a national alert from the president of the United States.

- Imminent or ongoing threats such as hurricanes, tornadoes or earthquakes.

- Child abductions or Amber alerts.

T-Mobile, Verizon (VZ, Fortune 500), Sprint Nextel (S, Fortune 500) and AT&T (T, Fortune 500) all stated that they would be likely to opt into the alert system if it is passed by the FCC.

"While we obviously need to review the details of the FCC's decision, we look forward to offering mobile emergency alerts to our customers," AT&T said in a written statement.

A Sprint representative said the company would participate if the FCC adopts the plan exactly as it was recommended by an advisory group.

A federal agency, yet to be appointed, would create the messages and information that would go to the participating cell phone companies, the FCC representative said. Once that agency is named, all carriers who opt into the system will have to meet the requirements of the system within 10 months.

Subscribers would be able to opt out of receiving the messages, according to the current plan, and carriers would be required to provide vibration or audio attention signals with a distinct sound for people with disabilities.

The alert system plan was generated out of an act Congress passed in 2006 that looked at emergency communications. The act directed the National Telecommunications and Information Administration, the Department of Homeland Security, and FCC and other agencies to work together to enhance and expand the capabilities of emergency communications in the United States.`