Jeff Bezos, chief executive of Amazon.com, is hoping that Kindle, an ambitious $399 e-book device recently introduced, will avoid the fate of previous attempts at the technology. Kindle, which Amazon spent three years developing, lets users wirelessly download best sellers for $9.99 each, and it is designed to be simple to use and comfortable to hold. Most significant, Amazon has made it easy to shop for and buy books through Kindle without using a computer. The device connects to a high-speed wireless data network from Sprint, and wireless delivery is included in the cost of books and other products. Downloading a book takes less than a minute.