More Americans than ever before are buying smartphones and using mobile data services like text messaging, games, email, mobile Internet, video, and ringtones. 
But while mobile media use has grown rapidly in recent years, mobile advertising has been slow to take hold, Nielsen Mobile reported in a white paper released Tuesday.
In the U.S., some 76.8 million mobile users recall seeing advertising on their phones, according to Nielsen, but 63% report encountering mobile ads only infrequently — once a month or less.  Meanwhile, less than two-thirds of website homepage page views feature …