• by Mark Walsh  @markfwal, November 18, 2010

Android tied Apple's iOS as the largest smartphone platform on the Millennial Media mobile ad network for the first time in October, with each accounting for a 37% share of impressions. Android's share jumped eight percentage points from 29% in September, while Apple's dropped nine from 46%. That's a 17 percentage-point swing.

Android's expansion was fueled by a 65% monthly gain in ad requests compared to 12% for iOS. If current trends hold, the Google mobile operating system should overtake iOS as the top smartphone OS on Millennial's network in November. Android has become the top-selling smartphone platform in the last six months, surging past the iPhone and Research in Motion's BlackBerry OS, according to recent Nielsen data.

Millennial previously reported that ad revenue generated by the Android device had already outstripped the iPhone for the first time in September, although it did not provide dollar figures.

Although Android still had a smaller impression share than iPhone then, Millennial said tighter ad supply combined with strong demand pushed up fill rates, click-through rates and prices on Android apps and mobile Web inventory. It also suggested that some advertisers were willing to pay a premium for Android placements to reach consumers across multiple carriers and first-time smartphone buyers.

The new Millennial report shows that BlackBerry increased its share slightly on the ad network to 20%, well behind both Android and Apple but far ahead of other smartphone systems including Windows and Symbian, which only had 2% each.

Apple remained the top phone manufacturer on Millennial's network with a 25% share -- and the iPhone was again by far the single biggest device, driving 16% of impressions. For the first time, Millennial included the iPod touch in its ranking of mobile devices, and the Apple media player debuted at No. 3, behind the iPhone and BlackBerry Curve, with 7.5% share of impressions.

The iPad is further down the list with 1.5% share, but ad requests generated by the Apple tablet more than doubled from September. About 4 million iPads were sold during the third quarter, helping to give the device a bigger presence on the ad network.

Samsung pushed ahead of Motorola to become the No. 2 manufacturer behind Apple with a 17% share. Motorola, however, maintained a roughly 15% share as a pair of Motorola devices, the Droid 2 and the Droid X both cracked Millennial's list of top 30 devices. The original Droid was the fourth-ranked device with a 6.7% share. Powering the Droid line and Motorola's resurgence in the smartphone arena, of course, has been Android.

Millennial says its network reaches about 80% of the U.S. mobile Web audience of approximately 80 million.