code: def _is_viable_phone_number(number):
      
      if len(number) < _MIN_LENGTH_FOR_NSN:
          return False
      match = fullmatch(_VALID_PHONE_NUMBER_PATTERN, number)
      return bool(match)
docs: Checks to see if a string could possibly be a phone number.
  
      At the moment, checks to see that the string begins with at least 2
      digits, ignoring any punctuation commonly found in phone numbers.  This
      method does not require the number to be normalized in advance - but does
      assume that leading non-number symbols have been removed, such as by the
      method _extract_possible_number.
  
      Arguments:
      number -- string to be checked for viability as a phone number
  
      Returns True if the number could be a phone number of some sort, otherwise
      False