According to the latest research from Nielsen, the launch of the iPhone 4S had an “enormous impact” on the percentage of new smartphone purchasers who bought an iPhone. Among recent acquirers—those who said they got a new device within the past three months—44.5 percent of those surveyed in December said they chose an iPhone, compared to just 25.1 percent in October. Interestingly, the same metric for Android buyers dropped over that same period, from 61.6 percent in October to 46.9 percent in December. In addition, 57 percent of new iPhone owners surveyed in December said the bought an iPhone 4S. Overall, 46 percent of U.S. mobile consumers had smartphones as of Q4 2011, with 60 percent of recent purchasers choosing a smartphone over a feature phone. [via Fortune]