From The RadioReference Wiki
Inmarsat provides telephony and data services to users worldwide, via special terminals which communicate to ground stations through twelve geosynchronous telecommunications satellites. Inmarsat's network provides reliable communications services to a range of governments, aid agencies, media outlets and businesses with a need to communicate in remote regions or where there is no reliable terrestrial network.
- Inmarsat std-C is a text messaging system that is in widespread use around the world, mostly among maritime users.
- A decoder for monitoring Inmarsat-C transmissions can be found here