Wall Street had expected the company to deliver quarterly earnings per share of 54 cents on $34.27 billion in revenue after the closing bell, according to consensus estimates from Thomson Reuters.
The firm posted a net loss of $4 billion, or 77 cents per share, in the fourth quarter, compared with net income $6.9 billion, or $1.31 per share, in the year-ago quarter.
AT&T also reported net subscriber adds of 1.9 million, beating estimates of 1.79 million.
Shares of the company rose about 2 percent in after-hours trading.
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"Over the last year, we've made several moves to significantly transform our business for the future," Randall Stephenson, AT&T chairman and CEO, said in a media release. "Our transactions with DIRECTV and Mexican wireless companies Iusacell and Nextel Mexico will make us a very different company. We'll be unique in the industry because we'll be able to offer integrated capabilities across a diversified base of services, customers, geographies and technology platforms."
The company also highlighted that its total wireless revenues were up 7.7 percent year over year to $19.9 billion. Within that figure, wireless equipment revenues increased 72.3 percent to $4.8 billion, the company said, as "more customers chose equipment installment plans versus subsidized devices."
The No. 2 U.S. mobile operator announced Monday that it would acquire bankrupt NII Holding Inc's wireless business in Mexico for $1.875 billion. The acquisition will help AT&T create the first-ever North American Mobil Service area to cover over 400 million consumers in Mexico and the United States. The deal is expected to go through by the middle of the year.
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Last quarter the company announced its wireless operating profit margin decreased as more customers signed up for "mobile share value plans."
As for the future, AT&T said it expects 2015 will see continued consolidated revenue growth, adjusted EPS growth in the low single-digit range, expanding margins and improving free cash flow and dividend coverage.
The company reaffirmed that it expects capital expenditures to be in the $18 billion range.
—CNBC's Reem Nasr and Reuters contributed to this report.