Of all handsets running on Android worldwide as of April 2010, 75% are in North America, 12% in Asia and 11% in Western Europe, according to the latest AdMob Mobile Metrics Report.
iPhone devices are more broadly distributed worldwide, but also had its greatest concentration in North America with 49%, followed by Western Europe (28 percent) and Asia (14 percent).
There was a 2:1 ratio of iPhone devices to Android devices in the US, but worldwide that ratio expanded to 3.5:1.