According to Nielsen’s numbers for October 2010, Apple’s iOS has passed RIM’s BlackBerry OS to become the most popular smartphone operating system currently in use in the U.S. The data jibes with both Canalys and NPD Group, which also put Apple in the No.1 smartphone spot in October. Nielsen’s Q3 market share data showed RIM with 30% and Apple with 28% of the market. After the first month of Q4, Apple holds 27.9% of the market and RIM sits close behind with 27.4%. Both companies lost market share to Google, which jumped from 19% to 22.7% in October. Considering Android’s rapid growth rate — which shows no signs of slowing — it’s a safe bet that Apple’s reign will be short-lived. At its current pace, Android should overtake the No. 1 position sometime in the first quarter of 2011.