(AP) More American households are ditching their old telephones: 4 out of 10 only use cellphones, a government survey shows.

That's twice the rate from just five years ago, although the pace of dumping landlines seems to have slowed down in recent years.

The Centers for Disease Control and Prevention has been tracking phone use for a decade, and the number of households only using cellphones had been rising by about 5 percentage points each year. Lately, the increases have been smaller and last year it only went up 3 percentage points to 41 percent of U.S. homes.

Why the slight leveling off? Experts could only speculate. The lead researcher on the CDC report, Stephen Blumberg, said it could be people are holding onto their landlines because it is part of their Internet and cable TV package. Or it could mean that we're hitting a ceiling for those people willing to completely abandon landlines, said John Palmer, a researcher at the Autonomous University in Barcelona, Spain, who was not involved in the report.

Some non-experts were surprised to hear that the change has slowed down a bit.

"We switched to only cellphones three years ago. The only time we would get calls on the landline was from telemarketers," said Justin Hodowanic, an 18-year-old college freshman from Atlanta.

Dan Warhola, 34, said he had a landline at his Columbus, Ohio, home but only because his security system was tied into it years ago when he bought his house.

"I couldn't even tell you what my (landline) phone number is," said Warhola, standing at baggage claim at Atlanta's Hartsfield-Jackson International Airport.

The CDC survey released Tuesday is based on in-person interviews in more than 21,000 homes during the last half of 2013.