(Images courtesy of AppleInsider)

The latest data from mobile ad agency AdMob is in, and it contains some surprising information -- including that 57 percent of the 44 million unique iOS-based devices tracked are from outside of Apple’s home turf.

AppleInsider is reporting that Apple was the top device manufacturer on the AdMob network in May, according to the mobile ad agency’s May 2010 Mobile Metrics Report released this week. Among the countries with the strongest growth for the iOS platform is Asia, Oceania and Western Europe -- in fact, the United States makes up only 48 percent of all iOS devices worldwide, with 28 percent from Western Europe and 15 percent from Asia.

The survey finds that 58 percent of iPad users in the month of May came from the United States, followed by a distant second in Japan with only five percent -- not surprising considering the device launch in Apple’s home country in early April and wasn’t rolled out internationally until late May. China and the U.K. carried four percent each.

As seen in the chart above, AdMob has tracked a whopping 29.3 million unique iPhones worldwide; including the iPad and iPod touch, the network found 43.8 million unique iOS devices. By comparison, all of the Google Android-based handsets combined clock in at only 12.7 million, despite have so many different manufacturers and models available.

One other nugget of interesting data from the AdMob report: It seems that iPhone users actually rely more on Wi-Fi than other smartphone users, with 24 percent of all mobile traffic in the U.S. being out of AT&T’s 3G data network. Perhaps the telco was right to start capping mobile data plans, using the excuse that said most customers use far less than 2GB of data per month?

Follow this article’s author, J.R. Bookwalter on Twitter