Android stayed atop its perch as the leading mobile OS on Millennial Media's ad network last month, though Apple continues to shine as the top device maker.

Looking strictly at mobile platforms, Millennial Media's June Mobile Mix report found Android on top with 54 percent of all ad impressions last month. In second place was Apple's iOS with a 26 percent share. Both results were little changed from May but showed Android's growing dominance since it overtook iOS on the ad network last December.

Rounding up the rest of the pack, RIM's BlackBerry OS took home a 15 percent share of all ad impressions, followed by Nokia's Symbian with 3 percent and Microsoft's Windows Mobile with 2 percent.

Millennial Media

Among the actual device makers, Apple held onto its leading spot with a 30 percent share of all impressions among the top 15 manufacturers, a number that includes the iPhone, iPad, and iPod Touch. By itself, the iPhone scooped up a 16 percent share, keeping it in the lead among the top 20 mobile phones tracked by Millennial Media.

With its overall device share growing 10 percent from May, Samsung took second place for the fifth month in a row. The company was helped by its Nexus S smartphone, which saw its ad impressions more than double over the prior month.

In third place was RIM with a share of almost 12 percent, down slightly from May, though its BlackBerry Curve phone achieved a 5.5 percent share among the top 20 phones, second only to the iPhone. HTC followed in fourth place with 10 percent of all impressions as its HTC ThunderBolt managed to squeeze onto the top 20 phone chart in 19th place.

For the first time ever, Millennial Media also looked at how people are now using tablets for tasks they previously performed via other devices. For the entire second quarter, 27 percent of tablet owners reduced the time they used the Internet on their PCs, 29 percent checked e-mail less often on their PCs, and 23 percent used their e-book readers less frequently.

The study also found that 27 percent of tablet users watched fewer videos on ther computers, while 19 percent watched fewer TV shows and movies on their televisions.