> Iridium has some advantages. It has coverage at the poles, where GEO sats typically do not. The mobile units can be small(ish) and handheld. But it also has some significant limitations. Datarates are in the 2400bps range. Latency goes all over the place due to the way the calls get routed through the constellation. Dropped calls are common.

I seem to recall the south pole base use multiple iridium phones in a aggregation setup as a backup data channel.