They claimed it will work on most existing phones, but they did caveat with "aspirationally" all over the place.

If it’s send-only than a satellite receiving a ping isn’t insane - they’re only 340 miles up.

It's not send only. It's a standard cell phone service.

I didn't hear any claims of "aspirationally".

No, it's will be using standard cell phones with no additional hardware on the cell phone.