This is a paradigm shift, as they say, with significant implications for politics and pollsters.

For the first time, the number of U.S. households opting for only cell phones outnumber those that just have traditional landlines in a high-tech shift accelerated by the recession.

In the freshest evidence of the growing appeal of cell phones, 20 percent of households had only cells during the last half of 2008, according to a Centers for Disease Control and Prevention survey released Wednesday.

…Further underscoring the public’s shrinking reliance on landline phones, 15 percent of households have both landlines and cells but take few or no calls on their landlines, often because they are wired into computers. Combined with wireless only homes, that means that 35 percent of households — more than one in three — are basically reachable only on cells.

The changes are important for pollsters, who for years relied on reaching people on their landline telephones. Growing numbers of surveys now include calls to people on their cells, which is more expensive partly because federal laws forbid pollsters from using computers to place calls to wireless phones.