AT&T reported a huge quarter Thursday morning, once again propelled by the success of Apple’s iPhone. The nation’s second largest wireless carrier activated a record 5.2 million iPhone units during Q3 2010 — a huge leap from its previous record of 3.2 million in a single quarter. 24% of those iPhone activations were new customers.

More highlights from the quarter include:

  • Record 2.6 million net subscriber additions (30% increase year-over-year)
  • 745,000 net postpaid subscriber additions
  • 321,000 net prepaid subscriber additions
  • 92.8 million total wireless subscribers
  • Record-low churn of 1.32% (down 0.10% year-over-year)
  • Consolidated revenue up 2.8% year-over-year to 31.6 billion
  • Operating income was up $100 million year-over-year but operating expenses were up $700 million

The real takeaway from AT&T’s impressive Q3 is unfortunately a negative one, even in the short term: the iPhone makes up a massive amount of AT&T’s business. Should the carrier lose iPhone exclusivity next year, which looks increasingly likely, the results could be disastrous.