Somebody uses VoIP?

Hello, everybody. I'd like to setup a VoIP system on my PC, but I'm not sure is it worth it? Maybe somebody could give me an advice or some links where I can learn more about this service? Here are some links that I've found, but they don't give enough information there Business VoIP VoIP Phone Systems VoIP for small business VoIP Phone Systems in USA
Thank you very much