Global Mobile Satellite System
The Global Mobile Satellite System (GMSS) is a general term referring to the selection of satellite phone providers available to private customers. It is a term analogous to PLMN, referring to wireless telephony (cellular) carriers, and PSTN, referring to traditional wire-based telephony.
As of 2008, the allocated GMSS carriers are:
- Iridium Satellite LLC
- Ellipso (a non-operational service, with no satellites launched)
- ICO Global Communications
In 1996, the ITU introduced country code +881 for direct international dialing of phones on a GMSS provider. (Inmarsat had already been allocated country codes +870 - +874.) The next digit following the country code is allocated (two at a time) to a particular GMSS carrier:
Satellite numbers outside the GMSS country code 
Inmarsat is a satellite-based communications provider, but it is primarily a maritime service and is not generally considered part of the GMSS.
Globalstar usually allocates subscribers with a local number in the country they are based rather than using their GMSS country code.
Iridium also uses an Arizona-based access number to call Iridium phones for those unwilling or unable to call the usually expensive GMSS number directly.