According to the latest data from mobile advertising firm AdMob, the iPhone accounts for 50% of all worldwide smartphone ad requests. The company’s newly-published October Mobile Metrics Report (PDF Link) also shows the iPhone accounting for more than 22% of requests from all handsets worldwide, making it the top handset model, followed by the iPod touch with 9.8%. In the U.S. market, the iPhone fares even better, taking a 55% share of all smartphone ad requests. Among the top handset models in the U.S., the iPhone is number one with 24.1% of requests—an improvement over its worldwide numbers—while the iPod touch again comes in second with 11.4% of requests, also an improvement over its international numbers. AdMob’s percentages are based on ad requests, impressions, and clicks, tracked over the more than 15,000 mobile web sites and applications to which the company serves ads.