An opendialing plan is one in which there are different dialing arrangements for local andlong distance telephone calls. This means that to call another number within the same city or area,callers need dial only the number,but for calls outside the area,an area code is required. In this situation it is customary to show the area code in parentheses,signifying that in some cases the area code is optional or is not required,as suggested byITU-T RecommendationE.123. The area code is prefixed by a trunk code (usually "0"),which is omitted when calling from outside the country.To call a number in Sydney,Australia for example: