Apple's iAd should end the year with about 21 percent of the US mobile advertising market, according to an IDC estimate. Google is expected to fall to 21 percent, down from 27 percent in 2009 when including results from AdMob, which the company only formally acquired in May. Yahoo is forecast to drop from 12 to 9 percent, while Microsoft should slide from 10 to 7, and Nokia from 5 to 2.
