Teardown of Possio Greta cellular GSM fax machine

Not sure if this is useful to off-gridders but I guess if you are in an area with voice towers that do not offer data, this could be useful.

I wonder if a software fax app on a GSM phone would be able to send faxes without needing data service. Or in fact, might it have to? Otherwise I guess if it were to use mobile data it would have to run over VOIP, perhaps with sketchier results.