Updated from 9:06 a.m. EST

Shares of Motorola ( MOT) plunged more than 20% Wednesday after the wireless giant gave weaker-than-expected guidance amid continued troubles in its mobile phone unit.

For the fourth quarter, the Schaumburg, Ill., company posted an adjusted profit of 14 cents a share, well below the year-earlier level of 26 cents, but a penny better than the 13 cents analysts were looking for.

Sales for the fourth quarter were $9.65 billion, up from $9.43 billion a year earlier and slightly above the $9.6 billion Wall Street was expecting.

"We are focused on aggressively rationalizing the company's cost structure and working to get Mobile Devices back on track," CEO Greg Brown said in a press release. "The recovery in Mobile Devices will take longer than expected and there is a lot more work to be done," he continued.

Looking ahead, Motorola expects to book earnings of about 6 cents a share, before items, in the first quarter. Analysts were looking for a dime adjusted profit.

The earnings shortfall is due almost entirely to continued losses in the phone business, Motorola executives said on an earnings call Wednesday. The executives said the company would continue to lose market share in the first quarter and declined to provide a longer range forecast for market share or break-even results in the mobile phone unit.

The No. 3 cell phone maker shipped 40.9 million handsets in the fourth quarter, close to the 41.5 million units analysts expected. But high costs and price cuts brought on another wave of red ink for Motorola.

Phone sales in the quarter were $4.8 billion, down 38% from last year, and operating losses plunged to $388 million from an operating profit of $341 million in the same period a year ago.

Motorola's handset unit ended the year with an operating loss of $1.2 billion compared to a $2.7 billion profit in 2006.

Investors have not been patient as they wait for Motorola's turnaround. Shares of the company have fallen by a third in the past week.

Hopes that the Razr 2 would fuel a recovery have been dashed, big customer Sprint ( S) has run aground and there are no new phones in the offing to suggest the company has found a new design to lift its fortunes.

Motorola's woes, which began two years ago with the Razr's fall from fashion, are becoming even more dire given the backdrop of a slowing economy and cooling growth in mobile-phone sales.

Shares of Motorola recently were down $2.82, or 23%, to $9.50.

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