Smaller rivals like Jumptap and Millennial Media are also gaining, according to IDC

U.S. only. Source: IDC via Bloomberg Businessweek

The pie chart at right is somewhat premature, given that it is IDC’s best guess — via
Bloomberg Businessweek
— of what the $500 million U.S. mobile advertising market will look three months from now.

But it’s an indication of how the winds have shifted. Apple AAPL , which had 0% share of the market before it bought Quattro Wireless in January and launched iAd in June, will end the year at 21%, according to IDC.

Where did that share come from? Chiefly from Google GOOG , Yahoo YHOO , Microsoft MSFT and Nokia NOK , according to the Businessweek piece.

IDC’s before-and-after numbers for the biggest losers below the fold.

Dec. 2009 Dec. 2010
Google 27% 21%
Yahoo 12% 9%
Microsoft 10% 7%
Nokia 5% 2%

. . .
[Follow Philip Elmer-DeWitt on Twitter @philiped]