A satellite phone is a mobile telephone which communicates using satellites instead of using cell towers.
Three major satellite phone networks are currently in operation:
The use of low earth orbit satellites helps minimize round-trip-time, which greatly improves the perceived quality of the phone call.
The Iridum network is able to provide complete global coverage. There is no spot on the Earth where you will not be able to receive a satellite phone call through Iridium.
The Globalstar network utilizes 40 low earth orbit satellites orbiting at an altitude of 876 miles.
The Globalstar satellite phone network provides coverage over most of the Earths land mass. This includes most of North and South America, Europe, the Middle East, Northern Asia, and Australia.
The Thuraya satellite phone network provides coverage over Europe, the Middle East, Central and Northern Africa, Central Asia and the Indian subcontinent.
Thuraya offers dual-mode GSM and satellite mobile telephone services, transmitting and receiving calls through each satellite's 12.25-meter-aperture reflector.
The Thuraya geostationary satellites utilize on-board digital signal processing to create more than 200 spot beams that can be redirected on-orbit, allowing the satellite phone network to adapt to customer demand in real time.
Satellite phone calls are routed directly from one handheld unit to another, or to a terrestrial network.
The Thuraya network has the capacity for 13,750 simultaneous voice circuits.