There are 66 active satellites in the Iridium constellation, orbiting the globe in low-earth orbits. At present, Iridium is the only truly-global satellite solution, with coverage over all ocean regions and the Polar regions as well.
In addition to handheld units, fixed-mount terminals offer reliable coverage and additional features. For instance, the Thrane & Thrane SC-4000 is a fixed unit that can accomodate a vessel's PBX via a standard RJ-11 jack, or up to 4 additional Iridium handsets connected directly to the base unit.