A satellite phone, satellite telephone, or satphone is a mobile phone that communicates directly with orbiting communications satellites. Depending on the architecture of a particular system, coverage may include the entire Earth, or only specific regions.
The mobile equipment, also known as a terminal or earth station, varies widely. A satellite phone handset has a size and weight comparable to that of a late 1980s or early 1990s mobile phone, but with a large retractable antenna. These are popular on expeditions into remote areas where terrestrial cellular service is unavailable.

A fixed installation, such as used shipboard, may include large, rugged, rack-mounted electronics, and a steerable microwave antenna on the mast that automatically tracks the overhead satellites.

Satellite Phone Geostationary services?

Some satellite phones use satellites in geostationary orbit. These systems can maintain near-continuous global coverage with only three or four satellites, reducing the launch costs. The major satellite system in civilian use is Inmarsat.

The disadvantage of geostationary satellite systems is that because the satellite is so far away (approx. 22,000 miles), a comparatively large antenna system is required for signal transmission and reception. The phone system must therefore be quite physically large that is similar to the size of terrestrial mobile phones in the past, compared to the current tiny terrestrial mobile phones.