Also (and this is only partially relevant) : Gizmo *is* GV now ;)

I was addressing the question of whether one could go data-only and not need a voice plan. I believe the method I outlined fits that model. Whether it's fits certain definitions of VoIP/sip or not, I don't know, but I don't think that's relevant to the topic at hand.

Well, unless I'm mistaken, you can hook your GV number to Gizmo account and use a SIP client on your phone. That way would not require a voice plan.