• by Mark Walsh  @markfwal, October 29, 2009

  AdMob's latest metrics report out today highlights some of the dramatic changes on the mobile ad network in the two years since it began releasing data. For starters the volume of ad requests it handles monthly has grown more than six-fold-from 1.6 billion to 10.2 billion, as of September. Those figures also represent a geographic expansion from 16 to 64 countries.

When it comes to phones, the Motorola Razr was the top U.S. handset in terms of generating ad impressions in Sept. 2007, with the iPhone no where in sight. Jumping ahead two years, the iPhone and iPod touch are the top devices and half the top 10 phones have a touchscreen and six have Wi-Fi capability and dedicated app stores.

The shift underscores the oversized role smartphones have come to play in mobile advertising though accounting for only about a quarter of U.S. Phone sales. Even so, feature phones like the Razr and Samsung Messager still account for about 60% of all U.S. ad impressions, according to AdMob.

Growing Wi-Fi use has also helped propel mobile ad growth, more than tripling in the last year. In September, 18% of U.S. ad requests came through Wi-Fi connections and 42% from Wi-Fi-capable devices.

The new AdMob report also shows phones using Google's Android operating system continues to make inroads on the iPhone, accounting for 17% of U.S. smartphone traffic, up from 13% in August. As with the iPhone, much of the traffic from Android-powered phones came from mobile applications.

Despite the strides made over the last two years, the total number of 10.2 billion ad impressions in September actually marked a 3% drop from August. Just a blip on the path to higher growth?