Android phones accounted for more than half (53%) the impressions on the Millennial Media mobile ad network in April, nearly double the 28% share generated by the iPhone. BlackBerry phones drove 16% of impressions.
Smartphones overall delivered more than two-thirds (68%) of impressions on the network, while feature phones and connected devices each accounted for 16%.
In a telling sign of how important they have become to mobile advertising, smartphones for the first time made up all of the top 20 handsets on the Millennial network last month. Of those 20, all but four were Android phones.
The iPhone, however, remained by far the top model, accounting for 20% of impressions, followed by the BlackBerry Curve (5%) and HTC Evo (3%). Apple was also the largest device manufacturer on the Millennial network, with 32.7% of impressions. Rounding out the top five: Samsung (15.5%), HTC (11.7%), Research in Motion (10.5%) and Motorola (9.8%).
In terms of overall impressions, including from tablets and other connected devices, iOS has seen the biggest growth this year -- likely driven by the popularity of the iPad. Total iOS impressions have increased 47% since January compared to 19% for Android.
When it comes to apps, Apple's iOS platform also drove half of in-app ad revenue versus 39% for Android -- a six-point swing in Android's favor from March. Google's launch of a revamped Android Market this month designed to make apps easier to find could help it expand Android's share of ad dollars from apps.
Of the 11% of app ad revenue not claimed by iOS or Android in April, 9% came from BlackBerry devices and 2% from all other platforms including Windows Phone 7, Symbian and WebOS.
The number of apps on the Millennial network increased by more than one-third (34%) in the first quarter from the prior quarter, while impressions from tablets and other connected devices increased 200%. Gaming remained the most popular app category -- representing 32% of impressions -- followed by mobile social networking, music and entertainment, mail/messaging and weather.
Wi-Fi continued to grow as a way for mobile users to connect, given "the increased popularity of tablet devices, coupled with smartphone owners using Wi-Fi to improve cellular coverage significantly," according to Millennial.
In addition to the 29% of impressions generated via Wi-Fi connections, the balance came through wireless operator networks: Verizon accounted for 19%, Sprint 11%, AT&T and T-Mobile, each 10%, "other" services 9%, MetroPCS and Cricket, each 5% and Boost Mobile 2%.