Those living in the USA will want to sign up for Google Voice and T Mobile service.  Using the number Google Voice assigns as your T Mobile My Fav number, all your calls incoming and outgoing will be completely free.

Any call to your Google Voice number will ring your cell phone under your Google Voice number.  By assigning this as your My Fav number with T Mobile these incoming calls will be free. 

This gets even better.  You can call your Google Voice number, assigned as your My Fav number and call any number in the USA for free.  When you dial your Google Voice number from a phone on your Voice account, you either listen to voice mail or press 2 to dial a call.  By pressing 2 you can dial any USA number and connect for free!  Or you can also use this to dial any international number and pay minimal fees! 

This service will be coming soon to the iPhone and is already available for the G Phone.  Google Voice plus T-Mobile will equal extremely cheap calling and allow you to take the cheapest plan with My Favs.