Google Voice now offers free calls to the US and Canada using the Google Voice Application. In fact, you can make calls to your relatives and friends in the US and Canada simply by logging into your Gmail account and clicking on the Call Phone button just right under the Chat panel on the left side of your Gmail screen:

VOILA! Just key in the area code and phone number of the person you want to reach on the typebox and click on CALL. And you can start chattering away. I tried this and I can say that the call quality is quite good. Much better than Skype, IMO. But this is dependent on your connection quality as well, so don’t expect superb call quality if you’re using an unstable internet connection.