G1 and iPhone ads have many of the same benefits as standard mobile-format ads, such as allowing you to deliver mobile-specific calls-to-action and reaching your audience when they're on the go. Showing ads on the G1 and iPhone also has additional advantages for your advertising. Users are performing a lot of searches on these devices, and searches are likely to go up during the holiday season. Last Christmas, the iPhone drove more traffic to Google.com worldwide than any other mobile platform.
Read more on Google's mobile blog