2011 was a flourishing year for Android as it moved ahead of everyone else in the mobile OS race. To start, it dominated with a 47 percent market share of device impressions last year, while iOS only had 33 percent, according to the latest Millennial Media Mobile Mix report, which looks at the entire year of 2011. Their positions switched from 2010, when iOS had 41 percent of the market, leaving Android with just 30 percent. That is to say, Android’s impressions are growing 504 percent year-over-year.

However, Apple remained the top manufacturer in Millennial Media’s platform for 2011, and the iPhone is still the top individual mobile phone out there. Samsung tails closely in the number 2 spot.

2011 also marked the decline of feature phones. The top feature phone was number 4 in Millennial Media’s list of top 20 mobile phones in 2010, but it slid to number 16 by 2011.

Another smartphone manufacturer to take note is HTC. They’ve been growing 79 percent year-over-year, and despite a tumultuous year HTC managed to be the number 3 manufacturer in 2011.

The year-in-review also provides an opportunity to break down the smartphone explosion of 2011.  Smartphone devices really started to explode last year, which became more noticeable last May. The smartphone accounted for 68 percent of all shares in the device OS mix, and 20 out of the top 20 mobile phones were already smartphones. As eMarketer puts it, “Momentum in the mobile device market has swung in favor of smartphones, led by the allure of Apple’s iPhone and the legion of now-viable competitors it has spawned.”

Data + smartphones = win for Wi-Fi

And with the rising data usage for smartphones and tablets, there was significant traffic that came over from WI-Fi networks.  And it’s growing 21 percent year-over-year, making up 27 percent of all impressions in Millennial Media’s platform.  It’s a trend that’s affected the entire mobile market, from wireless providers to the Wi-Fi networks themselves.  And in most cases, Wi-Fi is a welcome alternative to increasing data plans and throttled speeds.

“The growth of Wi-Fi can be attributed to the growth of Connected Devices on our platform and the increased sophistication of Smartphones. As the capabilities of Smartphones increased, the use of Smartphones for larger bandwidth activities also increased, like streaming movies and music; resulting in Carriers requiring consumers to connect to Wi-Fi for these activities.”

And it turns out the Steve Jobs was right about tablets. According to iSuppli, the number of tablet shipments more than tripled year-over-year, and it’s expected to continue doubling every year for the next four years.

In November’s Mobile Mix Report, Millennial Media pointed out that the Kindle Fire was starting give Apple some stern competition as its impressions grow at an average rate of 19 percent since launch. It’s expected to soar to hundreds of millions of impressions in the coming months.