Of course, all this data is only based on AdMob's network of advertisers, but it correlates well with the overall trends in mobile web use we have seen this year, including a recent study (PDF) by Nielsen Mobile, which saw the number of mobile Internet user in the U.S. grow from 30 million in May 2007 to 40 million in 2008.

One other interesting data point in AdMob's report is that in June, 24.3% of its ads were served to smartphones, up 22.4% since May. While Apple's iPhone is not the leading phone for mobile Internet use by far, it definitely has made a lot more people aware of the possibilities of the mobile web and encouraged them to consider buying smartphones over regular phones. For now, though, the most popular device for accessing the mobile web in the U.S. is still the Motorola RAZR.

Overall, these are encouraging numbers for anybody who is developing for the mobile web. While there used to be regular discussions if the mobile web could ever become a mainstream phenomenon, the last year has clearly shown that users are becoming increasingly interested in using the Internet on their mobile devices and as more users are shifting towards smartphones, this trend will surely continue for the foreseeable future.