It will start of with text messaged only. That should give you an idea about the throughput.

It's much closer to the SOS. They start with text messaging, which is much easier because it's low bandwidth and tolerant of delays. Voice can also be done at low bandwidth but its a bit harder to ensure things sound smooth. And then data, but I think this will only ever be low bandwidth like internet browsing, not tiktok or facetime. There's probably a reason they aren't boasting about the bandwidth they can achieve...