Rolling heads aren't the only bad news coming out of Motorola. The embattled U.S. handset maker has lost or sacked a suite of top-level executives in recent months, including its chief finance, marketing and technical officers and former president of mobile devices. Half its staff at a design center in Birmingham, England, may be next. Activist investor Carl Icahn recently upped his stake in the company to 6.3% and announced Monday that he is filing a suit to gain access to Motorola documents. Observers say the company hasn't launched a compelling phone in years and isn't expected to make a strong showing at a major upcoming industry conference, CTIA Wireless. Now analysts are warning that Motorola is at risk of sinking further in the closely watched global phone sales rankings, from No. 3 to No. 4. The slide would be the latest in a disturbing slump: Motorola lost the No. 2 spot to Samsung less than a year ago.