Android Ad Impressions Surge While Revenue Eclipses iPhone

Apple’s iOS remained the top operating system on Millennial Media’s ad network in September, but for the first time, ad revenue from Android (s goog) devices eclipsed iPhone-only revenue.

The figures show that Apple (s aapl) is still in the driver’s seat, with 46 percent of smartphone operating system impressions, though its dominance continues to erode. It offers the top hardware iOS products, gaining 30 percent of all impressions. The numbers come from Millennial Media, a privately held, mobile ad network that claims to have the largest reach and most ad impressions in the U.S.

Apple iOS is fighting an increasingly fierce battle with Android, and is trying to outflank it with iPads and iPods. But the sheer growth of Android in handsets — and soon tablets — will tighten the race even more. The overall picture shows that smartphones and tablets are indeed the future. Millennial found that smartphones overall increased their hold on ad impressions, growing 7 percent month over month, and now account for 58 percent of the device mix. Feature phones, meanwhile, experienced their largest month-over-month drop, decreasing 4 percent to 29 percent overall. Nielsen now predicts smartphones will eclipse feature phone handset sales in the U.S. by the end of next year.

Smartphone growth is being fueled in large part by the rise of Android, whose increasing revenue highlights the overall momentum behind the platform. Android ad requests have grown 1,284 percent since January, while iOS requests have grown 18 percent in the same period. Android’s share of the smartphone OS mix has grown from 6 percent in March to 29 percent in September, while Apple’s share has dropped from 70 percent to 46 percent during the same period. This is consistent with the overall sales growth for Android, which pushed past the iPhone in the second quarter.

It’s unclear if the Millennial numbers are affected at all by the launch of iAd on iOS in July or Google’s acquisition of AdMob in May.

RIM (s rimm) continues to be a player with 19 percent of smartphone OS impressions in September and five of the top 20 devices. Average monthly growth in the third quarter was 18 percent, ahead of the iOS at 10 percent.

Apple’s wild card has been the popularity of its iPad, which has been on a tear since its launch. IPad ad impressions have grown 156 percent in the third quarter, while its revenue has jumped 316 percent. The iPad is now the second biggest connected device in Millennial’s ad network, behind the iPod touch.

The future is clearly headed toward smartphones and tablets, and that puts iOS and Android at the head of the pack. Apple remains the top player, but the growth of Android overall and the ad dollars it’s generating should start to reorder the developer ecosystem as more programmers see increasing opportunities in the platform.

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