We’ve written how Amazon plans to challenge Apple’s iPad with its own Android-based tablet. New details indicate the devices will appear as soon as September, in time for the important U.S. holiday buying period.

The e-book maker plans to sell 4 million tablets in 2011, shipping between 700,000-800,000 units per month, industry publication DigiTimes reports, citing unnamed “Taiwan-based component makers.” The tablet will use Texas Instrument processors, with Wintek providing touch panels and Quanta Computer assembling the who package.

Earlier leaks indicate the Kindle-maker will offer to tablet versions: a 7-inch device codenamed “Coyote” for $349 and a 10-inch model for $449. Amazon will provide “streaming movies services” for its tablet users, according to today’s report. The Internet retailer recently was ranked just behind Apple in online video sales.