Nielsen report from last fall, and in recent Pew Research Center findings.
Penetration is one thing, and actual usage is another. A number of recent reports show distinct generational differences in both frequency of use, and in the types of applications and uses. Most of these reports, however, have yet to really establish that smartphone ownership and usage have had a serious impact on either TV viewing or Internet use on laptops or desktops.
The difference is enough that MBD's research director, Joline McGoldrick, indicated that online marketers are not only finding mobile as a growing segment of the advertising marketplace, but that marketers should take into account the emerging generational differences as well. Advertising placement on mobile is one of the fastest growing ad segments, with a 60% growth rate this year, and predictions that mobile will account for more than 20% of all ad revenues by 2018.
Source - Millennials Spend More Time With Mobile, Impacts TV Time, Mobile Marketing Daily