AT&T. is raising the prices and the allotments of its data plans for smartphones and tablets but only for new customers.The new plans will be effective from January 22, the Dallas-based company announced Wednesday.

The AT&T plans hike data charges as much as 33 percent. So customers who used to pay $15 for a 200MB plan will have to pay $20 a month for 300MB of data. Smartphone or tablet users will have to pay $30 for a 3GB plan (the previous plan was $25 for 2GB). For an extra 1GB of data, the customer already on plans of 3GB or higher, needs to pay $10 monthly, AT&T said.

Data usage is increasing at about 40 percent a year, said spokesman Mark Siegel, We want to give customers more data upfront.

AT&T's plans, however, still are comparatively cheaper than those of Verizon Wireless, the No. 1 U.S. carrier.

Verizon's cheapest plan is $30 for 2GB of data, which is 1GB less than AT&T's new $30 plan. Unlike AT&T and Verizon, Sprint Nextel, the No. 3 carrier,  and T-Mobile USA, No. 4, still offer unlimited data plans.

In June 2010, AT&T, the nation's second-largest mobile carrier, introduced tiered pricing and ended its unlimited data option. AT&T shares rose 11 cents to $30.44 in early Thursday trading.