NHIS has released the latest estimates of wireless-only households in the US and, to almost no one's surprise, the steady increase continues. As of June 30, 2010 26.6 percent of US homes had only a telephone, a sharp increase of 2.1 percentage points since December of 2009. Another 15.9 percent of homes report that they take all or mostly all of their calls on a cell phone even though they also have landline service. The demographics of the wireless only population remain pretty much unchanged—young people, less affluent, less likely to have health insurance, more likely to be Hispanic, etc.
Some us, and I confess that I had one foot in this camp, once believed that as this group aged and became more established they might gravitate back to landlines but there is little evidence to support that. As you can see in the graph at the right (blue line is for adults), if anything, the slope is steepening.
When you look at these numbers it's hard to fathom that anyone doing telephone research might still be calling landlines only, but I see evidence of it every day. Fortunately, there is an emerging body of high quality research that is extremely helpful with the design, costing, and execution of studies that include cell phones. That literature is nicely summarized in AAPOR's 2010 Cell Phone Task Force Report.