It'd be interesting to know whether this is uplink-only, like most devices of the Spot series of devices on Globalstar, or whether the iPhone can also receive acknowledgements from the satellite.
As far as I understand, Globalstar's downlink capacity is (or at least was) severely limited and also uses a different frequency band than their uplink.
That is a very important feature – knowing whether an SOS went through is extremely important in a life-or-death situation (for making the decision of whether to best stay put or try to climb to better signal etc).
PLBs are actually gaining that feature as well (by using Galileo as the forward path for the acknowledgement signal) for the same reason.
As far as I understand, Globalstar's downlink capacity is (or at least was) severely limited and also uses a different frequency band than their uplink.