When it comes to selling iPhones, AT&T Inc. (NYSE:T) remains supreme. A recent mobility report indicates that AT&T sold more iPhone 5 units than their top competitor, Verizon Communications Inc. (NYSE:VZ), during the third quarter.

Ralph de la Vega, mobility expert, discovered that AT&T Inc. (NYSE:T) sold about 1.3 million units. Verizon Communications Inc. (NYSE:VZ) only sold 651, 000 units. Overall, AT&T sold a total of 4.7 million iPhones. The overall number also includes sales of the iPhone 4S.  According to De la Vega, preorders for the sixth generation smartphone were high, but the supply was limited, and therefore had an impact on the numbers. He said that the minimal amount of units available led to lower than expected sales. He explained, “We faced significant supply constraints in the third quarter, which clearly affected net (customer additions).”

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Despite the fact AT&T Inc. (NYSE:T) sold all those phones, the company only garnered 151,000 new contract subscriptions. Both carriers posted disappointing numbers of new subscriptions.

De la Vega is positive that the numbers will go up soon enough. He said, “I feel very comfortable where we will be in a position to add more customers as (iPhone) supply becomes available.”  He also reminded us that the iPhone 5 launch isn’t any different than previous launches. He said that carriers usually see a large spike in sales once a new gadget launches and over time, sales start to slow down to a more reasonable amount.

AT&T Inc. (NYSE:T) sold 6.1 million smartphones this quarter, which is up from the 4.8 million a year ago. The iPhone is one of the keys to AT&T’s success, but it’s important to remember that the company still has to pay some heavy subsidies to Apple Inc. (NASDAQ:AAPL).

Apple Inc. (NASDAQ:AAPL) is still the leader of smartphones and it doesn’t look like that’s going to change anytime soon.  It’s evident that the company may have made a few mistakes regarding the supply of their iPhones, but no company is perfect.