Skype Questions

Anyone know anything about using Skype? I'm having information overload. Do you really have to have Skype credit to do SMS messages to phones in the US, even it's Local? I can do it for free with Google, but Skype's always running whereas Firefox is not. I guess I thought it would be free in Skype too. Well, it's still useful for free calls to Skype users. I have family that got into Skype, so I wanted to give it a try.