In its first full quarter of sales, the iPhone has already climbed past Microsoft’s entire lineup of Windows Mobile smartphones in North America, according to figures compiled by Canalys and published by Symbian.

You can't get Canalys' number's without paying a lot of money, so instead what many folks do is find some sucker who's willing to pay for those numbers and publish them. Symbian is often that rube, and so we have the numbers and they show something startling: in one quarter (maybe two), the iPhone had garnered 27% of US marketshare in the smartphone category.

Source- http://www.wmexperts.com/articles/iphone_2_in_the_usa.html