Source: Harjo Kompagnie, Direct ICT
var vPhoneNumber = arguments[0]
var vString = 'skype:' + vPhoneNumber + '?call'
if(utils.stringMiddle(application.getOSName(),1,7) == "Windows") {
application.executeProgram('rundll32', 'url.dll,FileProtocolHandler',vString)
} else {
application.showURL(vString)
}