http://www.pewinternet.org/2015/04/01/us-smartphone-use-in-2015/

10% of Americans own a smartphone but do not have broadband at home, and 15% own a smartphone but say that they have a limited number of options for going online other than their cell phone. Those with relatively low income and educational attainment levels, younger adults, and non-whites are especially likely to be “smartphone-dependent.”