SAN FRANCISCO (Reuters) - Amazon.com Inc took a $170 million writedown in the third-quarter largely related to its unsold stockpile of Fire smart phones as well as supplier commitment costs, Chief Financial Officer Tom Szkutak said on Thursday. The online retailer, which also issued a disappointing fourth-quarter outlook that sent shares down 9 percent in after-hours trading, ended the third quarter with about $83 million worth of Fire phone inventory. The Fire phone debuted this summer to both lackluster sales and reviews. Last month, Amazon cut the price of its phone to 99 cents with a two-year contract with AT&T. (Reporting by Deepa Seetharaman; Editing by Chris Reese)