Traders seem to be predicting a zero-sum game among the mobile providers. Growth by competitors raises questions about whether AT&T can top expectations, too. AT&T 's stock fell as much as 4 percent Wednesday and was down about 2 percent as of noon ET. Shares are down 19 percent year over year.

T-Mobile announced Wednesday that it added 2.4 million subscribers in the fourth quarter, crushing analysts' expectations of 857,000. Verizon also had a standout fourth quarter, and said Wednesday it added 650,000 new customers — well above analysts' expectations of 355,600.

AT&T is also reportedly preparing for a "significant round of layoffs," according to a report by Vice News, which cited internal documents obtained by the news outlet.

"We are hiring to meet the needs of the growth areas of our business. In fact, we hired more than 20,000 new employees last year and more than 17,000 the year before," AT&T told CNBC in a statement. "In cases where we do have to adjust our workforce, we take steps to lessen the effect on employees."

The company is in the midst of shifting from phones to an emphasis on streaming after its acquisition of Time Warner. What's now being called WarnerMedia is planning to release a streaming service later this year.

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