Summary:

Monthly figures out from Millennial Media once again show that Android is the most dominant OS on its mobile ad network — the mobile platfo…

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Monthly figures out from Millennial Media once again show that Android is the most dominant OS on its mobile ad network — the mobile platform from Google (NSDQ: GOOG) has held that distinction for 11 months now as dozens of Android-based smartphones continue to proliferate the market. But while there are definitely a good handful of handset makers that are benefitting from that Android popularity — HTC and Samsung among them — the handset maker that is still topping the charts for single most-popular device is Apple.

Millennial notes that in October, Android’s lead as the most popular platform on its mobile advertising network has grown, but not by much. It’s currently at 56 percent, compared to 54 percent two months ago.

That slight growth does not appear to have been at the expense of Apple and RIM (NSDQ: RIMM), which respectively have 28 and 13 percent platform shares. Those remained steady, while “other” decline by two percentage points. (Windows Phone and Symbian, for what it is worth, have held steady at one percent each.)

Apple, too, has held on to the lead it has maintained for more than year now: it is still the top mobile device maker, and still has the top mobile device, the iPhone. And its share remained steady as well, at 24 percent.

But it’s worth pointing out that Apple’s lead against other handset makers appears to be narrowing. Again, comparing this month’s results to those from two months ago, Apple has grown its share by 0.4 percent to 23.5 percent of all devices. The second-largest, HTC, is now at 18.11 percent, compared to 16.33 percent two months ago. And number-three Samsung has also grown its share to 17.24 percent compared to 14.55 percent previously.

What’s to explain that narrowed lead? It could be the continuous launches of new devices from the Android makers, against only one new device from Apple (NSDQ: AAPL). Or it could be to do with evolving user habits and the customer base grows. It could be simply a question of volume of devices on the market: that decline was also reflected in Apple’s last quarterly report, which noted a lower number of iPhones sold than some analysts had expected, even though it still reported sales of 17 million iPhones and 11 million iPads.

Mobile ad spend. Although iOS is behind Android by nearly 30 percent in terms of usage on the network, interestingly when it comes to ad spend, iOS continues to get a disproportionate amount of revenues, although they are slowly coming in line with the platform’s wider market share. Millennial notes that iOS gets 40 percent of ad spend, compared to Android’s 50 percent, with RIM at only six percent and the rest falling into the “other” category at four percent.

Media and entertainment remained the most-popular categories for mobile ads on both the Android and iOS platforms.

The very small shares given to RIM and “others”, including Windows Phone, raises some questions over whether those figures are actually universal, or whether they are do to with Millennial focusing its activities on Android and iOS.

But considering that Millennial is one of the bigger mobile ad networks, and given that mobile advertising remains one of the key revenue streams for mobile content — mobile ads are expected to bring in $1 billion in revenue this year — that doesn’t bode well for platforms like Microsoft’s Windows Phone, in terms of the message it sends to developers.

Depending on one’s risk-aversity, that could either spell a dead end, or an opportunity.

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