Wifi calling, at least with AT&T, and I suspect Verizon is the same, is just like normal calling when in the States, you're right, they have no clue where you are, but they probably do due to the IP address you are logged onto, BUT they do know where you are calling and this is where the charges come in. Call to the US, no charge as they are part of your plan, Calls to the Island, there will be a charge, just the same as if you were physically in the US