They did mention it during the keynote, but it's not automatic. It appears you have to open Find My and click to share your location over satellite each time. Might be wrong though, they didn't go into detail.
You can't even realistically point the InReach Mini at a satellite because it doesn't tell you where they are. At any time there's only a couple of iridium sats in view and they move quite fast across the sky.
But the device has an antenna with the right amount of upwards gain and the right polarisation to deal with that. For an iphone it's a lot harder to incorporate that.