A quarter of smartphone users rely mainly on their phones for internet access, according to a new study from the Pew Internet and American Life Project, that also found that more than one-third of all American adults have taken the smartphone plunge. In the center’s first stand-alone examination of smartphone use, it found that 33 percent of users said their phones were smartphones and 39 percent said their phones operate a smartphone platform such as iOS, Android, BlackBerry, Windows Phone or Palm.