AT&T, the largest U.S. phone company, will curb browsing speeds for its heaviest users on unlimited wireless data plans to cope with surging data traffic.

Starting Oct. 1, customers on an unlimited plan whose monthly use puts them into the top 5 percent of data consumption may experience reduced speeds until the end of that billing cycle, the Dallas-based company said today on its website. Normal browsing speeds will return once the customer begins a new cycle, AT&T said.

“This change will never impact the vast majority of our customers and is designed to create a better experience for all,” the company said. Heavy users who don’t want their speeds curbed can switch to a so-called tiered plan and pay more, AT&T said.

AT&T and other carriers are battling congestion on their networks as sales of smartphones surge and more people use them to download video and browse the Web. The company said the move to curb unlimited data plan users is designed to target those customers who typically use 12 times more data than the average smartphone customer.

“Even as we pursue this additional measure, it will not solve our spectrum shortage and network capacity issues,” AT&T said. The carrier said its planned takeover of T-Mobile USA Inc., which has yet to be approved by regulators, will address capacity problems.

AT&T spokesman Brad Burns declined to comment beyond the statement.

AT&T was unchanged at $29.26 at 4 p.m. in New York Stock Exchange composite trading. The shares have dropped less than 1 percent this year.

(Source: Bloomberg)