How's search as a mobile internet activity? The Utilitarian Life of the Mobile Internet at ClickZ cites stats saying it's the third ranked category in the US for June 2005 according to Telephia, behind email (done by 4.8 percent of mobile users) and weather (3.9 percent). Search is done by 2.9 percent of the mobile audience. As you can see, all categories have a small number of the 191 million estimated mobile internet users doing anything -- but when they do go online while on the move, search is strong.
Most likely category of users to do mobile search? Those aged 35-41 (32 percent). OK, that's the most likely category to do email and weather, as well, suggesting to me they've got tech savvy plus the money to spend on devices and access. But interestingly, search is the most likely mobile activity by 18-24 years olds over others, including email and weather.
Most popular mobile search site? Google, with 2.1 percent of the mobile internet audience reach. Yahoo comes next at 1.4 percent. But Yahoo Mail is the second most popular destination overall at 2.4 percent, and Yahoo Driving Directions makes the list with 1 percent reach.
The ClickZ article has all the charts; original charts and details from Telephia here (PDF file).