For phone numbers in a country, you can define time zone information based on the country or its area codes. Countries with multiple time zones should not have a country time zone, but rather multiple area code time zones. You can set either a country time zone or area code time zones, but not both types.
Note: The time zone information is not for mobile phone numbers or pagers.
When you set a time zone at the country level, you permanently delete all area code time zones, if any exist, for that country. If you want to switch from a country time zone to area code time zones, you must first delete the country time zone.
To define area code time zones, you create or update area codes for the country. The area code description is usually the city or region that the area code encompasses. Multiple area codes can have the same time zone. If you want to switch from area code time zones to a single country time zone, just set the country time zone.