EMarketer's new study shows the time U.S. adults spend daily using mobile devices (not including phone calls) has more than doubled in the past two years. And in 2012 alone, mobile device usage looks to grow nearly 52%, to about 82 minutes per day.

Last year "non-talk" mobile device use passed print as the fourth most-used major media.

As 2012 is shaping up, the ranking (TV is top, then online, radio, mobile, and print) stays the same. But while television and online are growing in use, broadcast radio and (especially) print are slipping. Even online (using non-mobile computers) is seeing the pace of its growth slow. 

"Mobile, by contrast, is growing quickly from a small base — and growth in time spent is also being boosted by fast uptake of smartphones and tablets, which have still penetrated only a minority of all consumers," eMarketer explains. "As more U.S. consumers continue to acquire these devices, and current owners shift more of their digital activities to mobile and portable devices, mobile is grabbing an ever-greater share of time with all media — potentially at the expense of faster online growth."

Ad dollars, as we've seen, have not caught up to these shifts in media usage. While U.S. adults will average 11.7% of their media time on mobile devices, just 1.6% of ad spending will go there.

Read eMarketer's summary here.