• by Mark Walsh  @markfwal, June 18, 2009

While the iPhone 3G S set to hit stores Friday, the long-awaited arrival of Apple's upgraded smartphone is topic No. 1 in the mobile world. But the latest metrics report from mobile ad network Millennial Media shows that in May the current iPhone slipped to No. 2 in mobile ad impressions behind the Samsung Instinct.

The Instinct from Sprint edged ahead last month with a 7.19% share of U.S. mobile impressions, compared to the iPhone's 6.54%. Not a huge difference, but in this instance at least, the Instinct lived up to its billing as Sprint's "iPhone killer." (The Palm Pre now claims that title.)

Among manufacturers, Samsung maintains a more commanding lead, with a 21.4% share of impressions compared to Apple's nearly 12%. Motorola in May pushed ahead of LG for third place and into a virtual tie with Apple at almost 12% as well. (Unlike rival mobile ad network AdMob, Millennial doesn't include impressions from iPhone Apps and non-phone WiFi devices like the iPod touch in its calculations.)

Millennial attributed the Instinct's surge in share of impressions to Sprint's success in cultivating a growing base of users who prefer a touchscreen device. That push continued earlier this month with the launch of the Pre. As a share of handset market, touchscreen phones overall increased 6.5% from the prior month to 27.8%.

The Millennial research also showed that advertisers are increasingly employing rich media ads (featuring video or inviting users to download an app or buy a ticket, for example) and custom landing pages to promote specific events like a movie premiere or product launch.

In other words, they're taking more of a direct response than brand-building approach to mobile marketing. That was also reflected in a 13.7% drop in the share of campaigns driving users to a permanent mobile site, "which is the foundation for long-term brand development via mobile," according to Millennial. But two-thirds of campaigns sent mobile users to specialized landing pages.