You'd need to either:
- create a C++ object with the required function, and declare it to your QML script so you can call that function
- emit a signal in QML, and link it to a slot in your C++ classes

Or more easily, use : http://doc.trolltech.com/4.7/qml-qt....ernally-method
so, just replace what you had with:
Qt.openUrlExternally(link)