Nielsen's Telecom Practice has a report out today with a projection that Smartphones will overtake feature phones in the US by 2011. "We are at the beginning of a new wireless era where smartphones will become the standard device consumers will use to connect to friends, the internet and the world at large." As you can see from the following chart, Q3 of 2011 will see Smartphones taking up more than 50% of the US mobile phone market.
Also of note is the increase of Wi-Fi use for Smartphone users that has jumped 10-fold (from around 5% to around 50%).