"Satellite mobile phones utilize satellites to communicate with landline, cellular, or other satellite phones in most regions of the world. Responders use satellite mobile phones for emergency communications in order to coordinate response and recovery efforts in remote areas, where there are no landline or cellular telephone networks, or in areas where existing networks are damaged or overloaded during a natural disaster (e.g., severe weather or earthquake) or a man-made incident, including potential chemical, biological, radiological, nuclear, or explosive events. Satellite mobile phones can help maintain command and control functions during an emergency when existing communications networks are not functioning. These phones are designed to be relatively rugged and simple to operate, but are more expensive than cell phones to buy and use. To provide emergency responders with information on satellite mobile phones, the System Assessment and Validation for Emergency Responders (SAVER) Program conducted a market survey."
Department of Homeland Security: https://www.dhs.gov/