Google Voice – Integration Guide

When are you consuming the minutes? In US (simplistically speaking), you pay when you are using your cell phone handset, both for incoming and outgoing calls.

If the call is not ringing your phone, but is using computer, I would say there would be no charge.

The backend architecture is the same. The Ggoogle Voice was an acquired company (Grand Central), which was slowly being integrated into Google architecture. Makes sense to not reinvent the wheel.

You don't have to use the cell phone either. Used to be you could route the call to Gizmo5 VOIP account and then connect directly to it over the internet. Now Google bought Gizmo5 as well (though my VOIP phone still works with it).

1 + 3. Your method should work. See here. (The comments indicate that it works for calling people too)

1. I believe that there isn't another way of figuring the numbers out.

I would note that there are some google voice native apps already back in the app store, as well as the official Google app is said to be on its way.