Shared codes - Sometimes area codes are shared by a number of local government entities to maximise their use. Some area codes are shared by multiple provinces, as is the case for former sub-provinces like Guimaras and Iloilo; newly-carved provinces like Zamboanga Sibugay and Zamboanga del Sur; or provinces with small populations like Marinduque and Quezon. In extreme cases, area codes are shared across an island like in Leyte and Samar, or even entire regions, such as with the Cordillera Administrative Region. In order to identify the call's point of origin, the three-digit telephone exchange prefix is checked.Since the Philippines employs an open dial plan, telephone numbers dialled within a given area code do not require the area code, excluding calls made from mobile phones or pay phones. When dialling other area codes, the domestic long distance access prefix - 0 - is added, but when dialling from overseas, the domestic prefix is not included. As such, a typical telephone number in Metro Manila and Rizal would look like this: