Motorola ( MOT) shares skidded to a four-year low Tuesday as investors braced for another big disappointment.

The Schaumburg, Ill., wireless titan is set to report fourth-quarter earnings before the bell Wednesday, and Wall Street fears that the numbers may have crumbled under a mountain of inventory.

With any Razr 2 phone-fueled recovery hopes dashed, a big customer like Sprint ( S) running aground and nothing new in the immediate product pipeline, Motorola's prospects are looking dimmer than usual, say observers.

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 growth in mobile-phone sales cooling fast .

A Cooling Trend
Mobile-phone industry growth hits the skids
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Source: JPMorgan

Motorola's earnings presentation will be the first for new CEO Greg Brown, who took over for Ed Zander late last year. Analysts are expecting the tech shop to post a pro forma profit of 13 cents a share on $9.6 billion in sales.

Motorola, which already fell to third place in market share behind Nokia ( NOK) and Samsung last year, is expected to have sold 41 million phones. But phone shipments may have slowed in December, creating a glut of unsold devices and another drop in market share.

Nokia's Rise and Motorola's Fall
Mobile-phone market-share forecast
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*Gartner Group
**Analysts' forecasts

Motorola was recently down $1.34, or 10.1%, to $11.99.