Google is now formatting AdWords text and image ads for Android and iPhone mobile browsers. The ads can include mobile-only calls to action, and can be created from standard Google ads run on the Web. The ads will also work on other phones with full HTML browsers in the future as they become available. (Both the iPhone and the Android G1 have full browsers based on Webkit).
Vy sticking with full HTML browser phones, the links in the ads can continue to point to regular Web pages and still work in a mobile context. Advertisers can also run one single campaign across the Web and advanced mobile phones, and see where they get the best response.
More at the Google Mobile blog.