Market research and analysis firm IDC has released some past and future shipment estimates for what it calls "smart connected devices," which IDC defines as smartphones, computers, and "media tablets" — a term the company uses to describe devices with screens larger than six inches. Not unsurprisingly, the biggest and fastest growing segment belongs to smartphones, which are expected to go from 494 million units last year to 660 million in 2012 (33 percent growth), and nearly triple to 1.16 billion units in 2016. What's remarkable, however, is this huge growth is small potatoes compared to the same growth over 2011, which saw smartphone shipments go from 305 million units in 2010 to 494 million in 2011 — a 62 percent increase in just one year.

According to IDC, worldwide unit shipments of all three categories of devices reached 916 million in 2011, but that's expected to grow by 20 percent to 1.1 billion next year, and more than double to 1.84 billion by 2016. PC shipments, on the other hand, are expected to grow at a much more modest clip of only about 8 percent annually. Lastly, tablet shipments are expected to show 13 percent annual growth over the five years, going from 69 million units in 2011 to 198 million in 2016.

So what's the reason for the huge growth in smartphone shipments? IDC says that "growth will be driven by Asia/Pacific countries, especially China, where mobile operators are subsidizing the purchase of 3G smartphones," adding that "in many if not all instances, the smartphone will be the primary connection to the internet." China has already become the biggest consumer of smartphones by volume, and many companies (including Apple) are moving in to take advantage of its huge addressable market. Add to that the rapid pace at which people in richer countries are replacing their devices, and the huge growth expectations no longer look so surprising.