According to Growing Wireless, “37 percent of teenagers, ages 12 to 17, have a smartphone, an increase from 23 percent reported in 2011,” via Pew Research Center (Tens and Technology, 2013):

Mobile access to the internet is common among American teens, and the cell phone has become an especially important access point for certain groups: - About three in four (74%) teens ages 12-17 say they access the internet on cell phones, tablets, and other mobile devices at least occasionally.

- One in four teens are “cell-mostly” internet users — far more than the 15% of adults who are cell-mostly. Among teen smartphone owners, half are cell-mostly. - Older girls are especially likely to be cell-mostly internet users; 34% of teen girls ages 14-17 say they mostly go online using their cell phone, compared with 24% of teen boys ages 14-17. This is notable since boys and girls are equally likely to be smartphone owners.

- Among older teen girls who are smartphone owners, 55% say they use the internet mostly from their phone. In overall internet use, youth ages 12-17 who are living in lower-income and lower-education households are still somewhat less likely to use the internet in any capacity — mobile or wired.

However, those who fall into lower socioeconomic groups are just as likely and in some cases more likely than those living in higher income and more highly educated households to use their cell phone as a primary point of access.
We can deduce some things from the Pew research: People who are “mostly” accessing the Internet via cell phone are probably not using it much for work or research. More likely they are using it for tweeting and texting, a social vehicle rather than a learning one. Janell Burley Hofmann, mother and author of iRules: What Every Tech-Healthy Family Needs to Know About Selfies, Sexting, Gaming and Growing Up, offers some thoughts re rules: 

No Devices at Dinner. Or any meals. The table might be the only 20 minutes we have all day to say, eyeball to eyeball, “What is it like to be you today, my dear one?”

No Double Dipping. If we’re watching a movie, eating in a restaurant or splurging on hot fudge sundaes, there will be no texting, scrolling, chatting or working (!!) at the same time. If we’re lucky enough to sit together, we owe it to each other to be fully present. Even if we feel squirmy.
It’s not just about kids. I am troubled by the fact that, at a seniors’ home I visit sveral times daily, staff are often checking their mail on handheld devices while they work.
Now, it might be quite legitimate—if, for example, the floor nurse has heard from the the medical clinic. But I’d be pleased to hear of a house policy that personal messages are not to be sent or received (absent an urgency) except on breaks—just as we would do with the telephone.
The main thing to make clear to teens is: Technical expertise is not, as such, a form of protection. Lots of evil morons out there are better than 99.99 percent of the planet at sheer tech skill. Playing it safe means using common sense, a weapon evil morons don’t necessarily have.
 

Denyse O’Leary is a Canadian journalist, author, and blogger.