• by Mark Walsh  @markfwal, August 25, 2009

The iPhone in July continued to dominate mobile devices as an ad vehicle, accounting for 12.2% of mobile ad impressions, up from 8.6% in June, according new monthly data from mobile ad network Millennial Media.

As the iPhone increased its market share in July, that of other top devices remained largely unchanged from the prior month. The Samsung Instinct was the closest runner-up to the iPhone, with 6.5% share, followed by the BlackBerry Curve, 5.6%, and the Samsung SCH-R450, 4.6%.

Impressions on the iPhone and iPod touch also increased 29% last month, though that figure was down from the 68% gain in June.

Among handset manufacturers, Samsung was still No. 1 with a 22.4% share of impressions, but Apple closed the gap with an 18% share, up from 16% in June. LG and Motorola essentially tied for third with about 11% each.

The Millennial data also showed that mobile advertisers last month relied more heavily on run of network and category-based campaigns in July, pushing down cost-per-engaged-user (CPEU) rates broadly across the ad network. Millennial surmised that the shift toward broader campaigns could be a seasonal trend before advertisers go back to more targeted efforts in the fall.

Campaigns driving traffic to mobile sites increased 12.4%, continuing a pattern over the last three months indicating more marketers are building and maintaining an ongoing Web presence. Conversely, campaigns sending users to custom landing pages fell by 9.3% in July but still accounted for more than half (52.2%) of campaign destinations overall.