I use Skype-Out for practically all my cross-border calls, most often between Switzerland, the U.S. , Canada, Germany, France, Japan and Brazil. Rarely do others even notice I'm not calling from a conventional land line. Like RumoredNow mentioned, It just requires that you have a fast and stable internet connection. The other side doesn't matter as they are just answering a normal telephone call.
I wouldn't mind if on startup, Skype quickly tested the internet connection and gave me some indication of expected call quality. That would be a handy feature when visiting areas with less than perfect internet infrastructure.