Skype works good for me. Skype user to Skype user free anywhere in the world.
Main features:
Free Skype-to-Skype calls. Call phones and mobiles, send SMS. Free instant messaging. Voicemail. Free video call. Forward calls to a phone when you're offline.
Skype to any phone number worldwide 1 or 2 cents a minute.
They also have a feature where you can get a phone number anywhere in the US and (many other countries) that rings in your own home in another country (Costa Rica for example). Friends in the same country as your number only pay a local rate to call you – and you pay nothing to answer the call.
Video calls is another feature available if you have a webcam. Skype to Skype totally free. Skype to non-skype number 1 to 2 cents per minute.
All you need is a head set and the free downloads, easy to fund by CC.
Other stuff like Walkie Talkies availavle.
http://www.skype.com/intl/en/useskype/
wil.