AdMob did it, JumpTap and Third Screen/AOL did it, now according to AdWeek, Google is "readying new options for advertisers to target iPhone owners directly." These are iPhone-specific ad units. According to the story:

In meetings with agencies, Google has presented a new option to show different ads in response to searches made from iPhones. The change, expected to be implemented shortly, means advertisers will be able to create an iPhone ad group as part of their regular search campaign, according to agency executives briefed about the modification.

This is hardly a surprise given how much more engaged iPhone owners are with the mobile Internet than users of other mobile devices -- even BlackBerry the market leader. 

Assuming the accuracy of the AdWeek report, we can expect it to be something of a model for Android ad that platform becomes more pervasive over time. 

___

I asked Google for a comment on the article and he's what I received:

As part of our ongoing commitment to help advertisers more effectively reach their target audience, Google is currently testing a feature that gives advertisers more control over how their ads will appear on mobile devices with full Internet browsers, like the iPhone. This feature is currently in a limited beta with a small number of advertisers.