Facebook has about 150 million mobile users, up from just 100 million in April, and is counting on cell phones as the key platform for the future, according to the social-networking giant's head of mobile products, Eric Tseng.

"Mobile is fast becoming our growth lever," Tseng told attendees at the MobileBeat 2010 conference in San Francisco on Tuesday. Facebook CEO Mark Zuckerberg had pegged the number of mobile users at 100 million at the f8 developer conference in late April. Facebook has about 500 million members overall...