The iPhone 3G has become the top device worldwide for mobile ad traffic, according to the latest mobile metrics report from AdMob.

The company offers banner and text ads to mobile devices, and it said requests from the iPhone have jumped from 28 million in July to 236 million in October. Overall, Apple's handset was responsible for 4.1% of the company's monthly ad requests.

The vast majority of these ad requests come from iPhone users in the United States, where the handset still trails Motorola's Razr. This data is solely based on AdMob's network, so it does not offer a comprehensive view of the entire market. But it does suggest that iPhone users are more likely to use their handsets for mobile Web browsing than other users are.

Outside of the United States, handsets from Nokia and Motorola dominate AdMob's charts. Handsets like Nokia's N70 and Motorola's Razr and Krzr are consistently used to access the mobile Web, according to the company's report.

As more and more customers purchase smartphones and mobile browsers get better, the market for mobile advertising is expected to swell in the next few years. Tevenue is projected to grow from $1.4 billion in 2007 to $10 billion by 2013. But the looming economic recession has some analysts predicting that advertising will be down in general, and the mobile ad market may be hit hardest.

But AdMob remains confident it can thrive, and the company served more than 5 billion ads in October. The advertising network continues to court high-profile clients, and it serves ads from more than 6,000 customers including Comedy Central, Cover Girl, Ford, Land Rover, and Toshiba.