Reuters: AT&T Inc will spend $565 million within 10 years to replace or buy about 15,000 vehicles in its corporate fleet with cars and other vehicles that run on alternative fuels, the company said on Wednesday. The U.S. telecommunications giant said the investment would be the biggest of its kind by a U.S. company and struggling Ford Motor Co would be a key beneficiary. AT&T Chief Executive Officer Randall Stephenson told the Economic Club of Washington that fleet modernization …