Google is now making available the ability to target the "iPhone and other mobile devices with full Internet browsers." This was spotted by Search Engine Watch (forums) and I became aware of it via SEO Roundtable. Here's the administrative screen:

Close up of iPhone targeting selection:

Images credit: SEW Forums

Google discusses the new targeting options in a blog post today:

You may have seen ads running on the iPhone and G1 already. That's because Google Search on these devices used to show desktop results pages modified for these phones. Recently, the Google mobile team launched new results pages formatted specifically for the iPhone. Now, advertisers will be able to display ads exclusively on these mobile devices, create campaigns for them, and get separate performance reporting. If you prefer not to show your desktop ads on these phones, you can opt out and show ads only on desktop and laptop computers.

And here's Google's discussion of mobile ad formats:

iPhones and other mobile devices with full Internet browsers is a device platform targeting option that appears in the campaign settings for your campaign. By using this feature, your standard text and image ads will be eligible to show to users of iPhones and similar mobile devices when they perform a Google web search or browse relevant pages in the Google content network. These ads do not currently show on the Google search network, except for those targeting Japan.

As the passage above indicates, the targeting will be opt-out for advertisers. But it now gives search marketers the ability to run parallel campaigns online and in mobile and assess their relative effectiveness.

Google originally was going to push most of its AdWords advertisers into mobile (absent an opt-out) but shortly thereafter reconisidered and pulled back, choosing not to show mobile ads (or relatively few). This move represents a return to the "mainstreaming" of mobile at Google. 

It indicates that that Google feels comfortable enough with the user experience and is ready to start monetizing mobile search (outside Japan) in a more aggressive way.