Millennial Media

Apple still gets 55% of mobile ad hits

But Android is gaining fast, up 690% since January according to Millennial Media

The business of selling ads on smartphones and other handheld devices is growing like gangbusters, but tracking it got a bit trickier after two of the biggest mobile ad networks were swallowed up -- AdMob by Google (GOOG) and Quattro Wireless by Apple (AAPL).

But the third, Millennial Media, is still independent and still churning out monthly snapshots of MORE