North American Numbering Plan - Wikipedia, the free encyclopedia

For example: 234-235-5678 is valid 234-911-5678 is invalid, because the exchange code cannot be in the form N11. (For non-geographic area codes like +1-800, 9-1-1 remains invalid, but other N-1-1 codes are valid exchange prefixes 123-234-5678 is invalid,

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