Apple’s iOS platform accounts for half of mobile apps revenue on Millennial Media’s mobile advertising platform, the firm said in its latest ‘Mobile Mix’ report for April. Revenue generated from apps on the iOS platform grew 6 percent month-over-month and represented 50 percent of the total apps revenue in April, the report said. Android revenue accounted for 39 percent and RIM 9 percent, while others – including Windows Phone, Symbian and Palm – accounted for just 2 percent combined. The total number of apps on the Millennial Media platform grew 34 percent from Q4 2010 to Q1 2011.

Gaming apps maintained the number one spot as the leading category on the network, representing 32 percent of app impressions in April. However, travel apps and sports apps – ranked ten and six, respectively – registered the strongest growth. Travel app impressions grew 91 percent in April, which the firm said “reflects the increased use of mobile as consumers research their spring and summer travel plans.” Sports grew 56 percent as consumers used their mobile devices to follow seasonal US sporting events such as the NBA Playoffs, NCAA Finals, and The Stanley Cup.

The iOS platform retained its apps revenue leadership despite strong growth in Android-based smartphones. Android maintained its position as the leading smartphone OS on Millennial Media’s network for the fifth consecutive month with a 53 percent impression share, a 10 percent increase month-over-month; stealing impression share from iOS (28 percent) and RIM (16 percent). Smartphones in total represented 68 percent of the firm’s “device OS mix,” while Android devices accounted for 16 of the top 20 individual devices.