Mobile ad network Millennial Media has released its monthly Mobile Mix report for July. The findings reveal at a platform level, Apple’s iOS remained in pole position, with a 55 per cent share of impressions. Android became the second largest OS on Millennial’s platform for the first time since the company began reporting its OS mix in August 2009. Android also had the largest increase of 8 per cent, representing 19 per cent of smartphone impressions. RIM was the third largest OS, accounting for a 16 per cent share of impressions.

iPad requests grew 327 per cent month-over-month, while RIM (BlackBerry) apps, representing 11 per cent of the US Developer Platform usage share in July, experienced the largest growth month-over-month of 9 per cent.

Music-related apps moved from the sixth position in Millennial’s Top Mobile App list in June to the number three spot in July, representing almost 9 per cent of app revenue on the network. Shopping and retail-focused apps jumped into the Top 10 Mobile App Categories for July at number eight, which Millennial says reflects a potential back-to-school trend. Gaming apps placed in the No.1 spot for the third consecutive month, accounting for 47 per cent of app revenue on the network in July.

Millennial Media’s network is comprised of more than 3,800 devices across all operating systems.