LAS VEGAS (AP) – AT&T Inc. is adding cell phones running Google's Android operating system to its lineup, bringing what could be the iPhone's greatest rival into the fold of the device's sole U.S. carrier.

AT&T's head of consumer services, Ralph de la Vega, said Wednesday that AT&T plans to sell five Android phones from Dell, HTC and Motorola during the first half of this year. De la Vega was speaking at an event Wednesday ahead of the International Consumer Electronics Show in Las Vegas.

Android is shaping up to be the strongest challenger to Apple Inc.'s iPhone – more than 30 million of which have been sold in the past 2 1/2 years.

With AT&T's announcement, the four largest U.S. wireless carriers will offer phones running Google's software. There are about 20 such phones on the market, including ones made by Motorola and HTC and Google Inc.'s own Nexus One, which was announced Tuesday.

On Wednesday, Sanjay Jha, AT&T’s co-CEO, introduced the Motorola Backflip. The new Android device features the company’s well-received Moto Blur UI on top of Android version 1.5.

The Backflip has a unique reverse flip design that acts as a kickstand for viewing media. The back of the touchscreen has a track pad for navigation of the device. A spokesman said the unique attributes of the Backflip are an attempt to offer developers a new set of features to exploit.

“Since introducing our first Moto Blur-based device, we’ve remained focused on differentiating the Android experience and bringing it to new carrier partners around the globe,” Jha said. “Backflip maximizes the multi-tasking and multi-functional potential of Moto Blur with its unique design elements, making it as smart as it is social.”

Beyond its quirky form factor, the Backflip doesn't stray too far from the Motorola Cliq. The phone comes equipped with a full HTML browser, 3.1-inch high-resolution touchscreen, 5-megapixel camera, LED flash, A-GPS, stereo Bluetooth and a 3.5-inch headphone jack, as well as up to 32 GB of expandable memory.

The Backflip will be available in North America, Latin America, Europe and Asia beginning in the first quarter. The company gave no immediate information on a U.S. carrier partner for the Backflip but did say the device supports the GSM band, which would make it a potential candidate for either AT&T or T-Mobile USA.

Given that AT&T just announced an impending Android release from Motorola, the Backflip could be on its way to that carrier.

– Wireless Week’s Andrew Berg and AP Technology Writer Jessica Mintz in Seattle contributed to this report