AT&T Inc. will stop letting new customers sign up for its unlimited Internet data plan for smartphones and iPads, hoping to ease congestion on its network by charging the people who use the most data more.

The move comes just in time for the expected unveiling of Apple Inc.’s new iPhone next week.
Current subscribers will be able to keep their $30 US-per-month unlimited plans, even if they renew their contracts. But starting Monday, new customers will have to choose one of two new data plans for all smartphones, including iPhones and BlackBerrys.

With the change, AT&T is adopting a carrot-and-stick approach to assuage the data congestion on its network, which has been a source of complaints, especially in cities such as New York and San Francisco, which are thick with iPhone users.

Subscribers who use little data or learn to limit their consumption will pay slightly less every month than they do now, while heavy users will be dinged with extra consumption fees.

Analysts said they expect the move to be quickly followed by other phone companies, which should be eager to avoid the trap of unlimited-use data plans. With no caps on consumption, data use could swamp wireless networks while revenue for the operators remains flat.