Google allows free calls => Providers lose revenue. Then you open a whole can of worms. Providers provide the 3G and 4G access. The providers could drop package

Google allows free calls => Providers lose revenue. Then you open a whole can of worms. Providers provide the 3G and 4G access. The providers could drop packaged deals with Android phones, or obscure usage of Google Voice through custom firmware - just a few possibilities. I don't see this as possible until Google can provide the telephony access itself, so it does not start unwelcome competition with it's own partners.