More than 32 million American adults, or about 16 percent, have now ditched their landlines for cell phones, up from 5 percent in 2004, according to a recent study from the Centers for Disease Control (CDC). In 2004, approximately 40 percent of U.S. households relied only on landlines. That number dipped to about 22 percent in 2007, according to the report. Homes with landlines and cell phones increased from 43 percent in 2004 to 59 percent last year.