Finally out of the beta-only invites, Google Voice is now officially out for the USA. Google Voice can link multiple numbers together and customize the way calls are received and sent to.
Here is a video on how Google Voice is handled on your cellphone:
And one for the feature I find most important, international calls:
You can go here to check Google's international rates.
To sign up for Google Voice, go here.
To download the Google Voice App for your Android cell phone, go here.