Can't imagine that the emergency SOS functionality will use 85% of their network, so it has to be other uses. The Find My functionality certain is one possible use case that they've discusses, but it's not clear when/how that will be used. Might be a "push to send location" manual function (which would take hardly any data), or it could be automagic (sending every X minutes when no cell service available).
Though I suspect there is more coming. Once the launch settles down, I wouldn't be surprised that with Apple's announcement of the service cost (beyond the initial free 2 years)... that something like 2 way messaging becomes available. To any iMessage compatible user, of course. As part of the paid feature set.
> or it could be automagic (sending every X minutes when no cell service available).
It wouldn't be automatic. If you watch the reveal today, they show how they avoided adding in a satellite antenna: it's communications to a satellite is weak and requires manually holding up the phone pointed at a specific direction (it appears the iPhone keeps an offline copy of ephemeris data so it knows where the satellites are located and can tell you exactly where to point).
Though I suspect there is more coming. Once the launch settles down, I wouldn't be surprised that with Apple's announcement of the service cost (beyond the initial free 2 years)... that something like 2 way messaging becomes available. To any iMessage compatible user, of course. As part of the paid feature set.