A week shy of Apple's Sept. 12 media event, Amazon has unveiled what is most likely going to be the iPad's biggest competitor with an 8.9-inch Kindle Fire HD with built-in 4G LTE data. It's $499, but contains 16 GB more than Apple's base-model iPad and already has the LTE modem. In addition, Amazon is offering a 250 MB-per-month data plan for the LTE Kindle Fire HD for $50 a year. That plan also includes 20 GB of cloud storage and a $10 credit in Amazon's app stor
