So it only works where wifi or partner data coverage is available. Cannot access cell networks? Ok, got it I guess.
I think it does... at least that is how I read it.
When not on wifi Google Fi will connect to "partner" cell network (LTE/3G/2G).
But I'm still not sure how different that is than my Android, since I'm pretty sure I can set it to make WiFi calls before it makes a cellar call. I suspect the method isn't unique it's going to be more unique due to being googlized through a lower, simpler payment plan with as many of the typical cell phone carrier billing tricks and gimmicks removed.