Funds run by Icahn bought 10 million Motorola shares this week, giving him nearly 10% of the Schaumburg, Ill., cell phone company. The purchases make Icahn the struggling company’s biggest shareholder, inching past the Dodge & Cox mutual funds.

News of the purchases sent Motorola shares up 6% in Wednesday afternoon trading. The move comes at a time when Motorola is trying to reinvent itself for the umpteenth time – a process that hasn’t been made any easier by Icahn’s prolonged involvement.

Icahn notified the company in early 2007 that he had taken a 1% stake. At the time, the stock was trading in the high teens. He promptly nominated himself for the board and set to work demanding a shakeup of the company, whose failure to find a successor for its popular Razr phone was sapping its financial strength.

After a heated back and forth, Motorola shook up its management, agreed to take two Icahn nominees on its board and to split itself up. Two years later, the company is still stumbling and fumbling, though sales of its Droid X phone are looking like a rare bright spot.

For Icahn and his many fans, the payoff on this three-year-long bet is yet to come. Even after a double off its 2009 lows, Motorola stock remains more than 55% below its level when Icahn first started rattling cages in Schaumburg. Caveat emptor, Icahn followers.