The Iridium Satellite system has 66 satellites that operate just over 400 miles up in a “Polar” orbit. These satellites are constantly moving, and could cause delays or dropped calls when attempting to make a call. You would have to wait for the next satellite to come into sight to make a call.
This system DOES give you FULL Global communication.
Inmarsat has 3 satellites up in “Geo-Synchronous” orbit (around 21,000 miles,) and are placed over the equator. Meaning, you must have a view of the “Southern Sky” from north American. These satellites are “Fixed” in orbit, and DO NOT move. They DO NOT work in the Northern or Southern Polar regions.
The “POR” satellite, is not used to do communications, but is more of a “Server” type of satellite.
Globalstar, Inc. is an American satellite communications company that operates a low Earth orbit (LEO) satellite constellation for satellite phone and low-speed data communications, somewhat similar to the Iridium satellite constellation and Orbcomm satellite systems. The Globalstar second-generation constellation consists of 24 low Earth orbiting (LEO) satellites in a “Polar” Orbit.
Thuraya satellite has NO North American Coverage.