Motorola said it is considering the sale or spin-off of its mobile phone business.

That the company was merely thinking about the move met with apparent approval from investors, who helped raise the value of Motorola stock by about one dollar, or 10 percent, as of mid-day.

Motorola’s mobile phone business is its largest unit. The company is the third-largest maker of mobile phones, but throughout the last year it has been steadily losing market share and stock value; the company’s shares were trading down about 55 percent since mid-October 2006.

The fall in stock value elicited a takeover attempt by one of the company’s largest stockholders, Carl Icahn, who made his name as a corporate raider in the ‘90s. Icahn had proposed breaking up Motorola into separate businesses. Motorola managed to fend off Icahn, but at the cost of former chairman Ed Zander’s job.

But with Motorola’s phone business still ailing, yesterday’s announcement shows that current chairman Greg Brown must at least explore the possibility of breaking up the company.

If there is a breakup, that could put all four units into play, including Motorola’s service provider operations, which makes products for the cable and telco industries.

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