def digits
      digitstring = ''
      [:area_code, :prefix, :number].each {|part|
        digitstring += self.send(part).to_s unless self.send(part).nil?
      }
      digitstring += " x#{extension}" unless extension.nil?
      digitstring
    end
def digits
      digitstring = ''
      [:area_code, :prefix, :number].each {|part|
        digitstring += self.send(part).to_s unless self.send(part).nil?
      }
      digitstring += " x#{extension}" unless extension.nil?
      digitstring
    end
TODO: Should #digits method include the extension digits at all?  Probably not
 with an 'x', anyway.