Not surprisingly, AT&T posted a significant loss during the fourth quarter, thanks to the hefty "breakup fee" it had to fork over after the demise of its T-Mobile acquisition deal.

The carrier did, however, activate 7.6 million iPhones and twice as many Android devices as the year before, resulting in AT&T's "best-ever smartphone sales quarter," the company said.

AT&T reported a $6.68 billion loss thanks to the merger snafu, as well as costs associated with its pension plans and smartphone subsidies.

Customers, however, are at least purchasing those smartphones. AT&T said sales of the advanced devices were up 60 percent from last year with 9.4 million devices sold. A good chunk of those, or 7.6 million, were iPhones. AT&T currently offers the free (with contract) iPhone 3GS, the $99 iPhone 4, and most-recent iPhone 4S; the carrier said the "majority" of fourth quarter sales were for the iPhone 4S.

AT&T did not break out how many Android devices it activated, except to say that "twice as many Android smartphones were sold versus the fourth quarter a year ago."

By the end of the quarter, 56.8 percent of AT&T's 69.3 million post-paid subscribers had smartphones, up from 42.7 percent last year and 32.8 percent two years ago. About 87 percent of those devices are on family or business plans.

AT&T also added about 311,000 tablet customers, but did not break out how many of those were iPads.

Overall, AT&T added 2.5 million wireless subscribers in the fourth quarter for a total of 103.2 million. Approximately 717,000 were post-paid customers, thanks in part to the iPhone 4S.

Rival Verizon also reported its earnings this week. The company was also hit by pension and subsidy charges. It sold approximately 4.3 million iPhones during the quarter, also more than half of its smartphone sales.

For more, see PCMag's review of the iPhone 4S and the slideshow below.