For the first time, Android ad revenue has exceeded the iPhone, according to a surprising study from Millennial Media.  The mobile ad network’s September MobileMix report is full of insight for the mobile world, noting Android’s unstoppable growth, which increased 26% for the month—1,283% since January.

Not surprisingly, Motorola made some gains, surpassing Samsung to become the second-largest device manufacturer in Millennial Media’s network.  This is a precedent for Motorola, but its market share within the network has been increasing steadily as of late.

Smartphones overall saw an increase in ad impressions, of 7% month-over-month, accounting for more than half of its ad impressions across all devices studied.  The iPad, however, is making waves, with a 316% growth factor in Q3, with ad impressions growing 156% during the same period.  This particular note is reiterated in Apple’s own numbers, released during the company’s earnings call yesterday, which noted high sales.

Not a whole lot has changed for the types of apps people like to download to their smartphones and mobile devices, with Games topping the list again.  Social Networking and Music follow, with a steady focus on entertainment.

This has been valuable information for advertisers and app publishers, with Millennial Media’s MobileMix report incorporating some additional device stats that we typically don’t see.  It retains this mobile consumption of entertainment-related apps, with Apple’s most popular game device, the iPod Touch, topping the list for most popular connected devices for Q3.  The iPad, Sony PSP and Sony Playstation were the next devices in line, which is encouraging for device manufactures looking to hop on this mobile gaming bandwagon.  As platforms like OpenFeint expand the capabilities of mobile gaming, we’ll see a great deal more development in this realm.