googlevoice? i've used google voice, from my phone to call friends overseas since it's much cheaper... not sure if that's what you're referring to though.
Google Voice is now available directly through the computer, through the Gmail webmail page. Pretty sure that's what jcheckers is talking about. I use it quite a bit when I'm working. Just make or receive a call with my headset. It's pretty handy.
I'm guessing more people use it in the US than the rest of the world; I've glanced at it on occasion but everyone I want to message or speak to still uses Skype; so Skype it has to be.