Question: how many different combinations of mobile phone numbers are there?
Answer: Each three-digit area code may contain up to 7,919,900 unique phone numbers: NXX may begin only with the digits [2–9], providing a base of 8 million numbers: ( 8 x 100 x 10000 ) . However, the last two digits of NXX cannot both be 1, to avoid confusion with the N11 codes (subtract 80,000).