I have skype. I use it not very often as I don't like it very much. Sure, you can call for free other skype users, but the connection is sometimes pretty bad, that I really prefer to pay for the phone having a good connection. I think, it depends on the internet speed you and the other person have how it works. Today it worked really good in my opinion. My father (he phoned me) said the oposite.
Just try it out and you'll see. It has good and bad sites.
And the privacy: Everyone can call me, but till now nobody I didn't know called, so who cares about it.