The fun thing about Iridium is that it's one of the few existing examples of satellite-to-satellite backbone links in space. The satellites are in polar orbits and talk to each other by directional point-to-point Ka band in space. This means that the whole network architecture (the first generation of satellites, not the ones imminently about to be launched for the new network) can relay all of its traffic through just one or two earth stations (Hawaii and Chandler, AZ).
This is why Iridium has kicked the ass of Globalstar, which was a bent pipe repeater satellite arrangement and relied on dozens of earth stations worldwide, also rendering it unable to provide service in polar regions and in the middle of oceans.
The only other telecom satellites that form backbone/trunk links in space are geostationary and military. The network architecture was WAY ahead of its time considering the design was finalized in 1996-1998 or thereabouts.