I have been using Skype for a while now and been very satisfied. Recently, Skype has expanded to include calls to POTS (Plain Old Telephone Systems).

You have to buy credits (minimum €10) and then can call. Interesting rates! Calling Germany from Switzerland is about 50% cheaper than using my discount telephone carrier. Voice quality is excellent.

And P2PVOIP continues to be free. Sounds good to me!