We did end up grabbing a used Ooma via fleabay & that whole deal has dragged me (kicking & screaming !!) through about a month of...stuff...not much learning though, as it is all very goofy.
I'm about to post here about that silliness in the thread entitled:
"Our latest Obi-related saga...continues !! "
Lotsa brainstorming in this thread, so prolly worth mentioning that smart speakers like Google Home Mini (at times <$3 on eBay) will easily CALL. Maybe soon it'll be possible to tell them to answer when a cell call is incoming.