Research in Motion Ltd.

The Curve, a new model of the BlackBerry device.

NEW YORK - BlackBerry maker Research in Motion Ltd. is introducing its third new model in less than a year, a mid-sized device geared toward consumers who might prefer a full keyboard for typing text rather than the abridged one on the popular Pearl.

The Curve, named for its smooth edges, will be offered first by AT&T Inc., though no launch date or pricing was disclosed in a news release Thursday.

The device has a front trackball below the screen to navigate its menus, a feature that RIM introduced last year with the Pearl as a replacement for its signature side wheel for thumbing through e-mail. With the Pearl's success, RIM also added the trackball to the 8800, the new version of its top-end phone for business users.

Despite its popularity, the Pearl may not appeal to users who don't like its unique keyboard design, which places two letters on each key and relies on predictive software to choose the desired letter.

The Curve has one letter per key, so it's wider from side to side than the Pearl though still small compared with many full-keyboard phones. The device, weighing 3.9 ounces, is 4.2 inches deep by 2.4 inches wide, and 0.6 inch thick.

Other features include a 2 megapixel camera with digital zoom and a flash, as well as a 3.5 millimeter stereo headset jack rather than the smaller earphone port found on most cell phones.