The total topped the previous record of 9.4 million sold in the same quarter in 2011.
The latest results suggested AT&T smartphone sales for all of 2012 will be about 26.7 million units, slightly ahead of its previous forecast of 26 million.
On Monday, AT&T rival Verizon Wireless said it had its strongest fourth quarter ever, with an increase in subscribers and a rise in sales of Apple Inc's iPhone 5 and other devices.
While smartphones help operators keep customers and attract new ones they also raise costs. Wireless service providers including AT&T pay hefty subsidies to handset makers so that they can offer device discounts to customers who commit to two-year contracts.
Wells Fargo analyst Jennifer Fritzsche said AT&T could miss her expectations for a wireless profit margin of 32.7 percent because of higher-than-expected smartphone sales.
Shares of AT&T were down 1.3 percent at $34.47 on Tuesday morning.
The company averaged daily sales of more than 110,000 smartphones that run on Apple, Google Android and Microsoft Window operating systems, AT&T Chief Executive Ralph de la Vega said in a statement.
AT&T will announce fourth-quarter results on January 24. Analysts, on average, expect earnings per share of 49 cents, compared with 42 cents for the same quarter last year, according to Thomson Reuters I/B/E/S.
© Thomson Reuters 2012
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