Smartphone ownership is growing by leaps and bounds in the U.S. But the devices’ continuing – and escalating – popularity isn’t due to busy mobile professionals snapping up the latest BlackBerry by the thousands.

A new study conducted by the Pew Research and American Life Project found that fully 35%of American adults now owns a smartphone. Although this is the first standalone study in which Pew has studied smartphone penetration, other studies put the rate of smartphone ownership at 20% last year, reports Tom Loftus in the Wall Street Journal’s Digits blog. The study also found that Android devices are the most popular choice, with 35% of smartphone users carrying them. BlackBerry and iPhone users each make up 24% of the total.

Other key findings from the Pew study:

• 83% of adults in the U.S. own a mobile phone
• 42% of those individuals say their phone is a smartphone
• The vast majority (87%) of smartphone owners access the internet or email through their device and two-thirds (68%) “do so on a typical day”
• One-quarter of smartphone users say they use their phone, rather than a computer, to access the internet

Details on that last finding about “cell-mostly” users show what smartphones’ growth really means – that people do not *need* a computer to be connected and smartphones represent a (relatively) inexpensive and dynamic way for people to stay connected.

The study reports: “While many of these individuals have other sources of online access at home, roughly one third of these ‘cell mostly’ internet users lack a high-speed home broadband connection.” WSJ’s Loftus foes a step further into the data, noting “Within this category of ‘cell mostly’ smartphone Internet users, the numbers were highest for people with no college education, 33%, and those making less than $30,000 a year, 40%.”

Simply put: smartphone use is growing exponentially partly because it offers people inexpensive, multifunctional and mobile internet access that they might not otherwise have. That’s the good news.

But the bad news is that the more smartphone users there are – the greater the likelihood that some percentage will use them in very un-smart ways. Another new study, this one from the University of Alabama at Birmingham, found that 35% of college students use mobile apps while driving. According to the findings, 35% of the 93 students surveyed said they “sometimes” use mobile apps while driving – while 10% said they “often” do so. Says study author Lauren McCartney, “The participants seemed to understand that using mobile apps while driving is dangerous, and some have even experienced motor vehicle crashes while using mobile apps, but they continue to do it.”

U.S. News & World Report notes that given the study’s small scale, the “findings should be regarded as preliminary” until confirmed by more thorough research. However, Pew’s study shows that smartphone ownership (and with it, mobile app use) is higher among younger people; 49% of 18-24 year-olds and 58% of 25-34 year-olds own smartphones.

Hopefully we won’t see Ms. McCartney’s findings confirmed by a sudden spike in distracted driving crashes on the ‘Bama crashes as hundred of students use their brand-new smartphones to clear the next level in Angry Birds.

Image via Ed Yourdon