you are correct, inReach devices can text by themselves(with no cell signal) and can be paired with a cell phone to make calls(I have the 66i), but not make calls by themselves.
I think I didn't write that clear enough :) I haven't used mine like this so far.. but you can pair the garmin to a phone(via the connect app) and make a call from the phone using the garmin as an antenna so to speak, you cannot talk or hear anything on it(the garmin inReach).
