Millennial Media (http://www.millennialmedia.com), an independent mobile advertising platform, said today that mobile connected devices like the iPad and Sony PSP displayed more than 20% of the giant ad networks’ ad impressions in March, a trend that could have far reaching impact on mobile advertising as these devices grow more popular.

Millennial Media decoupled the device and OS trending information from the company’s monthly Scorecard for Mobile Advertising Reach and Targeting (SMART); the new Millennial Media Mobile Mix will now complement the company’s monthly SMART report. The company’s mobile advertising network reaches 83% of mobile users in the U.S.

Millennial Media also reported that, for the first time, Android’s OS was in the top three in the ranking of smartphone impressions in March. Android OS impressions share increased 3% in March alone to bring the Google platform to a total of 6% of U.S. smartphone impressions for the month. Globally, Android impressions increased 72% month-over-month, while RIM also surged 25% globally, on the network.

However, the iPhone OS remains the leading OS on the Millennial Media network in March with 70% share of smartphone impressions. The operating system has maintained the leading OS position since Millennial began reporting OS mix in August 2009.

RIM remained the second largest OS for the eighth consecutive month with a 14% share of impressions; and four devices in the Top 20 Mobile Phone ranking. While Apple represented 40% of overall network impressions in March (top slot for the sixth consecutive month); manufacturers supporting Android enabled devices represented over 50% of the Top 15 Manufacturers. Samsung was firmly embedded as the second largest manufacturer on our network, with four devices in the Top 20.