Lazaros Kalemis is a loyal user of Apple's iPhone. But when he went to Phillies games at Citizens Bank Park earlier this year, his smartphone seemed to play dumb. He'd joke with friends that it was easier to find AT&T billboards than bars of service on his signal display.

No longer. The wireless-phone industry may be facing a "data tsunami" in network demand, as Nielsen analyst Roger Entner describes it. But AT&T says it has finally solved bandwidth problems at the ballpark that have plagued it since last year.

AT&T officials say they have installed a state-of-the-art system that adds the equivalent of nearly three cell towers within the 45,000-seat stadium. They say the system quadruples the channel capacity available to fans of the Phils, who have sold out every home game so far this season.

Kalemis watched the team lose a recent heartbreaker to the Mets after AT&T's system was finally up and running. But his iPhone, at least, didn't frustrate him.

"It worked perfectly," said Kalemis, chief executive officer of Alpha Card Services, a Huntingdon Valley credit card processor.

AT&T has faced an engineering and a public relations challenge at Citizens Bank Park this year, both partly of its own making.

The nation's second-largest wireless provider is the exclusive carrier for the iPhone, a data-hungry device that encourages its owners to access the Internet and use thousands of specialized programs, or "apps."

The result has been a surge in demand from iPhone users that taxed AT&T's network. And it shows its stresses most obviously at places such as "the Bank," where an estimated 5,000 to 10,000 iPhone users might congregate more than 80 times a year.

AT&T added to its technological problem by promising a fix as the season began. When the fix hadn't materialized by the midseason break for the All-Star Game, subscribers were frustrated.

"It's been our one sore spot," said Dan Lafond, AT&T's regional vice president and general manager.

Some improvements over the off-season mitigated the problem, Lafond said, as has the strategic use of mobile cell sites. But he said he received constant reminders that the system was overloaded from friends and family, as well as from Phillies staffers who use AT&T.

"They give feedback. Feedback is a gift," Lafond said with a smile.

To fix the ballpark's problems, AT&T turned to a Medford company, Intenna Systems Inc. And because the Phillies did not want to turn the entire park into an AT&T WiFi hot spot - an approach the company was allowed to take at the San Francisco Giants' ballpark that bears its name - it had to be done with ordinary cellular technology.

Lafond and Intenna's chief executive, Christopher Lange, showed off their design this week to a reporter and photographer, after a "soft launch" earlier this month that was monitored on computers by about a dozen Intenna and AT&T staffers.

Lange said the system was a twist on a decade-old technology known as a "distributed antenna system" and could prove to be a model for other large venues. He calls its key new feature "antenna sculpting": Each of 132 antennas throughout the ballpark is narrowly targeted to serve a confined space, such as a single section or two of seats.

In many cases, the "sculpting" makes use of the building's own superstructure. To minimize bleeding of radio signal into adjacent sectors, for instance, antennas have been placed against steel girders. Others are inside mailbox-shaped metal hoods that limit the radio waves' spread.

Lange said the ballpark had been carved into eight sectors, each equipped with at least a dozen antennas that elsewhere in the region might serve six or more square miles. (Upper-deck fans still get their signal from three nearby cell towers, but they have fewer fans to share it with.)

AT&T's competitors, particularly highly rated Verizon Wireless, have likely enjoyed witnessing its troubles at the ballpark.

"AT&T has to speak for itself. But our focus is on planning to stay ahead of demand, and we've been able to do that very well," said Verizon Wireless spokesman Sheldon Jones.

Lafond said they should be careful not to gloat. He said that AT&T was the first carrier to face a dramatic spike in data demand posed by smartphones, but that other carriers would face similar spikes from new smartphones, especially those that use Google's popular Android platform.

In the first half of 2009, the average iPhone owner used 275 megabytes of bandwidth per month - five times that of the average BlackBerry user and nearly twice as much as used by other smartphones, according to Validas L.L.C., a Texas company that tracks wireless billings.

In the first half of 2010, iPhone average use rose to 357 megabytes per month, Validas said. But demand from other non-BlackBerry smartphones soared, from 150 megabytes per month last year to 410 megabytes.

Jones said Verizon Wireless was up to the task. "The bottom line is there's a ton of usage, and that's only going to grow."

Contact staff writer Jeff Gelles at 215-854-2776 or jgelles@phillynews.com.