Great news! Skype just released the news that they would provide free calls to US and Canada landlines (regular phones) and mobile phones till the end of the year.I have been using the free PC to PC Skype calls to chat with family members in China for quite some time already, and the sound quality is always pretty good as long as both ends are using broadband connections.
The best feature of Skype is that it now supports Video chatting using the 2.0 version on Windows (unfortunely no video chatting yet on Mac OS X). The interface is pretty simple and easy to use. My grandma even knows how to use it now
Have a try and enjoy!