Maybe everyone already knows about this, but I didn't.
http://www.talkatone.com/
I have a friend that uses it and it seems to work great. Basically you download the app on your smart phone, and then you can make calls for free whenever you are connected to wifi even if you don't have a phone service. Obviously it's not good for all your calls since you won't always be around wifi, but if you have an old smart phone lying around and want an extra line for something this works great.
http://www.talkatone.com/
I have a friend that uses it and it seems to work great. Basically you download the app on your smart phone, and then you can make calls for free whenever you are connected to wifi even if you don't have a phone service. Obviously it's not good for all your calls since you won't always be around wifi, but if you have an old smart phone lying around and want an extra line for something this works great.