That’s the finding from the Centers for Disease Control, which has fallen into the odd role of being the federal government’s best leading-edge indicator of how many Americans don’t have landlines at home. The CDC research says the cell phone only count crossed the 20% line very fast – up nearly three percentage points since the previous report, six months earlier. The data is from late 2008 and no doubt the CPO percentage has kept growing. In 2003, just 3% of U.S. homes had no landline phone. What’s driving the changeover? Demographics. Younger Americans can’t imagine life without a cell phone. And, says the CDC – the recession. That’s making Americans think harder about household budgets, and most folks now have cell phones anyway. The 20% mark means that Arbitron’s going to have to hustle to keep pace in both diary and PPM placements. Even though reaching CPOs is more expensive than finding landline homes.