That's true, though real world performance is often more like 350kbps. The Iridium NeXT series satellites and second generation network are a fairly recent thing to go into production use in the past couple of years, before that, an individual iridium terminal was limited to about 2400 bps with v42bis compression. There were some famously weird multilink PPP bonding solutions used in Antarctica with four separate Iridium modems and antennas.