Fewer homes subscribe to broadband Internet service than they did two years ago, according to a new survey, the first sign that the cord-cutting phenomenon that has plagued cable television may be spreading. Meanwhile, smartphone ownership continued to expand, as more people are relying solely on mobile Internet connections.

Although the decline uncovered in the Pew Research survey was modest -- 67% of homes had broadband this year down from 70%  in 2013 -- the results marked the first time in decades that the reach of the wired Internet shrunk among households. Some 13% of households reported that they are "smartphone only," up from 8% in 2013.

If the trend continues, cable companies like Comcast (CMCSA) and Time Warner Cable (TWC) may have to rethink some of their strategies for coping with cord cutting among television viewers. The big cable companies have said they'll be able to make up for lost TV revenue by charging more for broadband Internet connections, imposing usage caps and offering online TV.

Television cord cutting continues to increase, as well, the survey found, continuing a trend echoed in myriad other reports. Only 76% of households pay for television, Pew found. Of the remainder, 15% have cut the cord and 9% are so-called cord nevers, who never signed up in the first place.

The motivation for eliminating broadband connections appears to be similar to the rational for getting rid of cable television -- money.

Among households that did not have broadband, cost was by far the biggest issue, with 33% saying the monthly charge was too expensive and 10% citing the cost of a computer. Some 12% said a smartphone could do everything they needed, 10% said they relied on options outside the home and 5% said service was unavailable or speed was too slow. Another 16% gave some other reason and 14% gave no reason.

Smartphone-only households were far more likely to be young. Almost one in five people aged 18 to 29 said they had just a phone, while 16% of those 30 to 49, 11% of those 50 to 64 and just 7% of those 65 and older said they had one phone.

Pew surveyed 2,001 people aged 18 and older from June 10 to July 12. The survey included people interviewed on landline phones and mobile phones and had a sampling error level of 2.5 percentage points.