If you want some data to back you up when your middle-schooler tells you that "Everybody has a cellphone," Forbes.com has some. Citing Nielsen Mobile research, it reports that "46% of US tweens (ages 8 to 12) use cellphones, but only 26% own them" and about 20% are using parents' hand-me-down phones. The 20% who don't own them borrow them from Mom or Dad. "About 50% take their parents' phones more than three times a week." Nielsen says that 8.5 is the average age when kids start borrowing parents' phones, and 10 or 11 is when they start owning their own. Ages 13-17 is when "phone use soars," with about 77% ownership in that age range. And how is the bill footed? Family plans: 65% of tweens. Prepaid, pay-as-you-go plans: 30%. "By age 18 to 24, most pay for their own mobile usage."