Cell phones vs. landlines from the CDC
Take this report on "wireless substitution," ie households that rely on cell phones rather than landlines, from the Centers for Disease Control and Prevention’s National Center for Health Statistics (NCHS) .
You might ask, "Why does the CDC care about who has cell phones and no landline?" The answer doesn't seem to be because they are tracking brain cancer from cell phones (Phew...) It turns out that when the agency conducts the National Health Interview Survey, they ask for a phone number for follow-up purposes. And they ask if this number is a landline, and if anyone in the household has a cell phone.
These questions yield some interesting answers, showing the rise of the wireless-only household, particularly in young adults renting with a non-related roommate.