As an intermediate user I use Skype to call Australia, UK and Spain and it works perfectly. Now to be honest there are other specialised offers such as the ones mentioned here that are perhaps cheaper and more flexible but there is something Skype has that can't be bettered - the network effect of multiple users and the free skype-to-skype calls.

At 0.03 CHF a minute to most places in the world its also pretty cheap. 15 CHF credit ususally lasts me 2 or 3 months! I have never had a problem with call quality.