A comparison of app usage across the three types of devices in October, not surprisingly, showed the iPhone (and iPod Touch) firmly in command of the field, according to new data from mobile ad network Millennial Media.

In addition to offering the most apps -- 115,000 to 13,000 for Android phones and 3,100 for BlackBerry devices -- the iPhone/iPod also had the most monthly downloads, with 100 million compared to 20 million for Android and 300,000 for BlackBerry.

Apple device users on average download 11 apps per month -- three times more than Android users and six times more than BlackBerry owners. In terms of click-through rates on in-app games, the iPhone had the highest rates across the social, entertainment, utility and navigation categories, at 0.5%, 3%, 8% and 5%.

Android, however, had the best click-through rate in the games area, where it also led with the highest proportion of new apps year-to-date through Nov. 1. It should be interesting to compare these figures six months or a year from now, with a slew of Android phones coming in 2010.

Market research firm iSuppli estimates that 10.7 million phones worldwide will run Android next year, up from 4.5 million in 2009. That will be equal to almost half the projected 22.3 million iPhones in the market in 2010, up from 18.7 million units this year. So Android should close the gap in app usage in the next year. How much is another question.

In its monthly tracking of click-through destinations, Millennial has also added application downloads to the mix. It found that 29% of campaigns drove users to download apps, the second-most-common destination after marketers' own mobile sites. Twenty-one percent of campaigns sent people to custom landing pages and 4% to some type of expanded rich media.

During October, Samsung regained the lead as the top device manufacturer on Millennial's network, based on impressions generated, after losing the top slot to Apple in September. Samsung devices accounted for 23.5% of impressions compared to 21.7% for Apple. But the iPhone itself remained the top device, with a nearly 12% share, more than twice that of its nearest competitor, the BlackBerry Curve.

Overall, smartphones represented 36% of impressions and regular phones, with 64%. Millennial said it reached 51.7 million people in October, or 80% of the 61.4 million U.S. mobile Web users.