WASHINGTON (MarketWatch) -- AT&T Inc. on Wednesday became the first major U.S. wireless company to move away from unlimited Internet plans and introduce metered billing, providing a future template for how the industry bills customers.

Executives at AT&T and Verizon Wireless have talked for months about the need to switch to metered billing as a means to reduce congestion and better manage their mobile networks. Heavy data usage by a tiny percentage of customers occasionally has clogged networks and reduced the quality of wireless service for other subscribers.

Dallas-based AT&T T, +0.74% appears to have suffered more than any other domestic carrier, because it's the exclusive U.S. provider of Apple's AAPL, +1.50% popular iPhone, whose customers tend to use much more data than other subscribers. About 3% of AT&T's smart-phone customers account for 40% of smart-phone data usage, the company said.

Yet metered billing won't increase costs for most AT&T customers, since very few are heavy data users. The vast majority might even save money.

In AT&T's case, 98% of customers use less than 2 gigabytes of data -- the cap set for the company's new $25 monthly plan. Also, 65% of AT&T customers use less than 200 megabytes of data a month, the limit set for a new $15 plan.

"A lot of people use less than they think they do," AT&T spokesman Mark Siegel said. Customers will be warned via text or email if they approach their limit and they can check their usage easily with their phones, he added.

The $25 "DataPro" plan, with 2 gigabytes of data, will replace AT&T's unlimited $30 plan starting on June 7. Two gigabytes is the equivalent of 4,000 Internet page views, 10,000 emails without attachments or 200 minutes of streaming video, according to AT&T.

DataPro customers that exceed the monthly cap would be charged $10 for each additional gigabyte of data.

Current iPhone customers would be allowed to keep their unlimited data plans and even renew them, at least for a while. AT&T would face class-action suits if it tried to change the terms of existing contracts, lawyers say.

AT&T also will offer a $15 "DataPlus" plan for 200 megabytes of data, in an effort to get more customers to sign up for wireless Internet service. The reduction drops the company's cheapest voice-and-data plan to $55 a month from $70.

The company said 200 megabytes is the equivalent of 1,000 emails without attachments, 400 Internet-page views or 20 minutes of streaming video. DataPlus customers that exceed their limit would be charged an additional $15 for another 200 megabytes.

The tethering option requires customers to sign up for the DataPro plan and pay an additional $20 a month. Subscribers could then use their phones as modems to hook up their laptops to the Internet. Tethering will become available after Apple releases its newest iPhone operating system later "this summer," AT&T said.

AT&T is also offering mobile customers free access to 20,000 Wi-Fi hotspots around the country.

Pitfall of success

Wireless companies introduced unlimited-data plans several years ago to persuade customers to upgrade their voice plans and spend more money. Millions of customers leaped to sign up, especially after the iPhone hit the market in mid-2007, but the resounding success of those plans has also put greater strain on mobile networks.

Carrier plan to add more capacity in coming years, but they are faced with the threat of increasingly congested networks unless they do a better job in managing data traffic.

Metering billing could improve overall network performance by discouraging so-called "data hogs" -- the small number of customers who account for the bulk of data usage.

"It's that 2% they are really trying to isolate," analyst Chris Antlitz of Technology Business Research said. "They are really eating up the bandwidth."

A Verizon Wireless spokesman declined to comment on AT&T's shift, but senior executives have said they were exploring metered billing. Dick Lynch, Verizon's chief technology officer, said in an interview with MarketWatch in January that the industry needed to eliminate unlimited data plans and bill customers based on usage, just like water and power companies.

FBR Capital Markets analyst David Dixon said he expects Verizon to soon follow suit, with the entire industry eventually moving to a metered model.

"Clearly, the current unlimited data usage model in the U.S. market is not profitable in the long term as data usage is expected to continue," he wrote in a report.

How soon that transition takes place is unclear. Some carriers such as Sprint Nextel Corp., with fewer customers than AT&T or Verizon, have enough network capacity to keep selling unlimited-data plans.

Indeed, Sprint S, -5.00% cut the price of its unlimited-data plan last year in an attempt to win market share. In a recent MarketWatch interview, Chief Executive Dan Hesse said Sprint had plenty of network capacity for now.

"They can take their time," pointed out Antlitz at Technology Business Research.

Sprint could not be immediately reached for comment.