Online ad network Millennial Media released their mobile device stats for March (slightly more detailed PDF version). The data is collected from visits across their network and includes both smart phones and tablets.

Overall, smart phones comprised 64% of visits to sites on the network, up from 62% in February. Tablets like the iPad and other “connected devices” were 17% of visits up from 14%. And the share for feature phones dropped to 19% from 24% in February.

Android leads in the smart phone segment, 48% to 31% for Apple. No break-down was reported for the tablet section in March but in February Apple’s 80% share dominated Android’s 17% take.

Most interesting, Millennial reports app market share by revenues. Apple leads, of course, taking 47% of all revenue in March. But Android, with a 36% share, was much closer than I expected. Could be that this is revenue solely from advertising but it’s not clear from the report.