In a surprising shift, adults appear to be choosing wireless smartphones for Internet access over Comcast and other wireline broadband providers, according to a study released Monday.

The Pew Research Center report described both a national decline in traditional broadband homes and a growth in smartphone-only households.

Nationally, broadband-wired homes fell to 67 percent this year from 70 percent in 2013, the study said. Smartphone-only households rose to 13 percent from 8 percent over the same two years.

The most pronounced changes are taking place among African Americans, Hispanics, and low-income individuals. According to Pew, almost one-fifth of African Americans rely only on smartphones and wireless services such as T-Mobile, Boost, Sprint, or AT&T for Internet access, up from one-tenth of African Americans in 2013.

"We were surprised in the consistency of the shifts," John Horrigan, senior researcher at the Pew Research Center and author of the "Home Broadband 2015" report, said Monday.

"Household budgets are tighter than ever, so it has become attractive for people to go smartphone only," he added.

He would not call the shift a trend, but rather a "pattern that's worth watching," Horrigan said.

Experts note concerns. Smartphone-only individuals face extra charges if they spend too much time online - particularly watching online streaming - and exceed monthly data-consumption caps. Other online activities, such as job searches or banking, can be difficult because of small screens.

The Pew study's two-year period covered a time when Comcast, one of the nation's largest residential Internet providers, expanded its discounted Internet Essentials program for poor families with schoolchildren in the Philadelphia region and throughout its cable-franchise areas. Comcast offers the service for $9.95 a month.

The Philadelphia company agreed to expand the Internet Essentials program during negotiations for its city cable-franchise renewal agreement, which City Council approved this month.

Philadelphia - the poorest of the nation's 10 largest cities - consistently ranks below national averages in Internet access. Monday's Pew report did not list the percentage of smartphone-only households by city.

In the Philadelphia region, Verizon Communications provides both high-speed wireline Internet access through its FiOS service and smartphone Internet access through its wireless division.

Bobby Henon, the Philadelphia councilman who led the Comcast franchise-renewal negotiations for the city, said the Pew report "confirms that 43 percent of individuals who don't have broadband say it's because the cost is too high. The City of Philadelphia leads the nation in the right direction when it comes to making Internet access a priority for its citizens."

Hannah Sassaman, policy director for the advocacy group Media Mobilizing Project, said the Pew report shows "why it is vital that our cities push hard to expand broadband competition and hold hometown providers like Comcast and Verizon accountable to provide high-speed, affordable access to all low-income people."

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