Amazon.com’s e-book reader Kindle 3G with special offers is now the company’s top-selling e-book device, according to media reports on Wednesday. Amazon revealed in its quarterly earnings report that the ad-supported version costs 139 U.S. dollars,  50 dollars cheaper than the comparable Kindle 3G, and costs the same as a Kindle with Wi-Fi connectivity. The advertisements will appear only in screensavers (which appear when the reader is in an idle state) and at the bottom of the home screen, so they don’t interrupt readers. “Since AT&T agreed to sponsor screensavers, Kindle 3G with Special Offers is now our bestselling Kindle device,” Amazon’s press release said. Having zoomed past the earlier Sony Reader, and kicked off a wave of competition including the Barnes & Noble Nook and the Kobo E-Reader, Kindle is believed the most popular dedicated e-book device on the market today.