The Center for Disease Control and Prevention on Wednesday became the unusual source for a study which shows that cellphone-only homes now outnumber landline-only homes for the first time. About 20.2 percent of homes use only a handheld for calls in later 2008 versus 17.4 percent that only use a landline phone. The shift is credited mostly to a steep drop in the number of those relying only on hardwired connections, which fell from 34.4 percent in 2005. In contrast, cell-exclusive homes jumped from just 7.3 percent over the same time span.

The influence of cellphones grows in the study when including those who depend almost solely on their phones despite having both types. An estimated 14.5 percent took the majority of their calls on cellphones as of 2008.

The CDC notes that the demographic change likely has its roots in the age of the users. The likelihood that a given person will use only a cellphone drops off significantly after age 30, plunging from 41.5 percent of those in their mid-to-late 20s to 21.6 percent of those between 30 and 44 years old. Those who rent or live with roommates are more likely to use only the wireless option than those who own a house.

While not mentioned in the study, the mix is likely to steer further towards phone-only homes through the expansion of smartphones, which are seeing much more use at home courtesy of hardware and apps better-suited to use outside of work, such as iPhones and BlackBerries.