A satellite phone is a telephone that communicates via artificial satellites. Because it does not rely on terrestrial base stations, it can make calls in areas beyond mobile phone coverage, such as mountainous terrain, open sea, deserts, and polar regions. When terrestrial communications infrastructure is destroyed during a disaster, satellite phones continue to function, earning them the designation of "last-resort communication."
Among the satellite phone services available in Japan, three are especially well known. Iridium uses 66 low-earth-orbit (LEO) satellites at approximately 780 km altitude to cover nearly the entire globe, including the poles. Thuraya uses geostationary (GEO) satellites at approximately 36,000 km altitude, primarily covering Asia, the Middle East, and Africa. Inmarsat also uses GEO satellites and has strengths in maritime communications. LEO satellites are closer to Earth, so latency is about 20-40 ms, enabling natural conversation. GEO satellites have higher altitude, resulting in latency of about 540 ms, which creates a noticeable delay in conversation.
In BCP (Business Continuity Planning) at municipalities and companies, satellite phones are treated as the fallback for the moment terrestrial lines become unusable. During the Great East Japan Earthquake, terrestrial communications infrastructure was devastated across wide areas, and satellite phones were the only means of communication in some regions. Learning from this, municipal disaster response centers, hospitals, and lifeline operators such as electricity and gas utilities keep satellite phones on hand as emergency provision. Handsets and call charges are both more expensive than regular mobile phones, but there is no alternative for ensuring communication during disasters.
In the 2020s, satellite communication stopped being the exclusive domain of dedicated handsets. Apple offers satellite-based Emergency SOS on the iPhone 14 and later, so in countries and regions where the feature is supported, a user can call for help from outside mobile coverage. In Japan, KDDI and Okinawa Cellular launched "au Starlink Direct" on 10 April 2025: au smartphones connect directly to SpaceX's Starlink satellites, and where there is a clear view of the sky, text messages can be exchanged even outside the coverage area. Neither arrangement works like a dedicated satellite phone that can carry a call at any time; both come with conditions on the handset and the location. Together with emergency call numbers, check Emergency Phone Number Guide to review communication options during disasters.