NEW YORK — In time for the widely expected launch of a new iPhone model, carrier AT&T is pulling in the reins on data usage by its customers with smart phones and iPads.

The sole U.S. carrier of the iPhone is introducing two new data plans, starting Monday, with limits on data consumption. They'll replace the $30 per month plan with unlimited usage that it has required for all smart phones, including the iPhone.

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. The new plans will take effect just as Apple is expected to unveil the next generation of its iPhone Monday.

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 fees. One new plan will cost $25 per month and offer 2 gigabytes of data per month, which AT&T says will be enough for 98 percent of its smart phone customers. Additional gigabytes will cost $10 each.

A second plan will cost $15 per month for 200 megabytes of data, which AT&T says is enough for 65 percent of its smart phone customers. If they go over, they'll pay another $15 for 200 megabytes.