NEW YORK » The flow of customers into AT&T’s wireless stores slowed further in the latest quarter, putting the company far behind rival Verizon Wireless.

AT&T Inc. today said it added a net 151,000 new customers on contract-based plans from July through September, the lowest number for that period since at least 2003.

The Dallas-based company is blaming short supplies of the iPhone 5, which launched a week before the end of the quarter. But that didn’t hold back Verizon Wireless, which last week reported adding 10 times as many contract-signing customers as AT&T did.

AT&T said the shortage of iPhones meant that most of them went to people who were already AT&T customers. Only 18 percent of the 4.7 million iPhones it activated in the quarter went to new subscribers, the lowest number yet.

AT&T suggested that it suffered in comparison to Verizon because it launched its new data-sharing plans later in the quarter. Verizon launched “Share Everything” just before the start of the quarter and said it prompted people to add lots of extra devices to their plans. AT&T waited until August to introduce “Mobile Share” and was less aggressive about it. At Verizon, “Share Everything” was the only choice available to new customers, while AT&T kept its old plans alongside the new one.

AT&T’s quarterly net income was $3.64 billion, or 63 cents per share, nearly unchanged from $3.62 billion, or 61 cents per share, a year earlier.

For the latest quarter, analysts expected earnings of 60 cents per share.

Revenue was also essentially flat from last year, at $31.46 billion. Analysts expected $31.57 billion.

Comparisons to last year were affected by the sale of AT&T’s phone book business in May. The unit was profitable but shrinking, so AT&T sold a controlling stake to a private equity firm for $950 million.

When subtracting the phone book business from last year’s results, AT&T’s earnings rose about 2 percent in the latest quarter, propelled by the wireless business, and revenue grew nearly 3 percent.

AT&T shares rose 13 cents to $35.13 in premarket trading.