Depends on your phone and coverage. I've seen zero bars and apparently connected. More often I see zero bars and not connected, usually has a line through the signal indicator.
Where I live, there's resistance to adding new towers, so our dead zones are pretty consistent. One part of town has very spotty coverage from all networks, but has some wifi that works a bit. Otherwise, there's a couple places where network B has no coverage, and others where network C doesn't. Last I tried, network A was hopeless at my house, but I assume it still has holes in the coverage.
Where I live, there's resistance to adding new towers, so our dead zones are pretty consistent. One part of town has very spotty coverage from all networks, but has some wifi that works a bit. Otherwise, there's a couple places where network B has no coverage, and others where network C doesn't. Last I tried, network A was hopeless at my house, but I assume it still has holes in the coverage.