If you initiate and receive all calls on your cell phone with Google voice as a default, are you using cell phone minutes or is it counted against your data plan?

Google Voice calls made on your cell phone use your minutes. It is possible to use Google Voice with a SIP client on your phone to make calls on your carriers data network or over wi-fi and not use minutes.

If you initiate and receive all calls on your cell phone with Google voice as a default, are you using cell phone minutes or is it counted against your data plan?