Area codes in Mexico do not begin with zero.

Telemarketers can use their PBX (switchboard) to block their actual number; they often substitute 999 as their phony area code. There is NO real 999 area code anywhere in the US (nor is there a country code 999 anywhere on Earth).

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No, there is no area code +1 999 in North America (USA, Canada, etc.).

Country code +999 is reserved for an unspecified future global telephone service.

In North America, general purpose area codes are area codes that are available for assignment as geographic area codes; in other words, all unassigned area codes that are not reserved for other purposes. Area codes ending in '11' are unusable due to conflict with N11 short codes such as 911 and 711. Area codes with the second and third digit the same are reserved as "easily remembered" codes such as 800/888/877/866/855/844 toll-free and 900 premium numbers. Area codes with '9' as the middle digit are reserved for future expansion. Most other unassigned area codes in the range 200 to 999 are general purpose area codes.