Social networking is quickly making the jump to mobile as more U.S. smartphone users turn to their devices to check social Web sites, a research study found. By the end of this year, nearly 82 million U.S. mobile users -- more than a quarter of the country\'s mobile population -- are expected to use a social networking site on their phone at least monthly, research firm eMarketer reported. By 2014, eMarketer estimates, nearly half of the total U.S. mobile population will be mobile social networkers. Facebook is leading the way as nearly 70 million people will access the site from their phones each month this year, the study found. By 2014 about four in 10 mobile users and nearly two-thirds of smartphone users will check Facebook on mobile devices, eMarketer said. The study was based on the analysis of survey and traffic data from research firms and regulatory agencies, historical trends, company-specific data, and demographic and socioeconomic factors, the firm said.