What's so significant about Google Voice as an iPhone app?

How does Google Voice determine what number I am trying to call when I call from the the GV iPhone app?

• When I use GV from the iPhone app, my phone dials a number. But how does it determine what number I am trying to call? I assumed that the app sent a piece of data that tells them what number I was calling but it works even when I shut off both wifi and cellular data on my phone.

• Answer:

  I have a bunch of things which makes me believe that its a bit of mapping and using data to know which number to call... Here is what my info is based on. I looked at the number google voice called when I called my friend. It seemed to call the same number every time I called her. I then asked her to check when she called me, it wasnt the same number my app called, but it was constantly one number her app would call when dialing me. I also have noticed that Google voice fails if calling a new number which i havent called before and I dont have data it fails. So here are my guesses. Google Voice maps your number, a google number and the calling number. They probably keep this map constant for frequently called people and that is why you can call your friend who you usually call without data It sends a tiny data packet to google with the number you want to call when working with a new number and gets back data on which number to call I could be verrry wrong... but I could also be right :)