Iridium is the only satellite network which provide truely global coverage including the North- and South-pole. The network consist of 66 satellits orbiting around the Earth in a 780 km distance. This very short distance is what makes it possible to use very small antennas to reach the satellit. Iridium is among the world leading satellite companies within handheld satellite communication and is used by mountain climbers to circumnavigation of the globe to the large merchant vessels.
Iridium manufactures their own hardware and this give them the advantage of making the new satellite service backward compatible. In 2015 they will start the launch of a new network called IRIDIUM NEXT. This new satellite network will give more capacity and faster download rates. If you buy today, you do not need to worry, your equipment will work after 2015 as well.
NEWS regarding GMDSS 17.October 2018.
New IMO agreements opens for use of Iridium for GMDSS, per January 1st. 2020.