About 14% of US households are now mobile-only, compared with 12.3% who are landline-only, according to MRI's "The Birth of a Cellular Nation" report.

Few households these days are without mobile phones. So the fact that mobile-only households outnumber landline-only households is not exactly a herald of doom for wired phones.

"This milestone is a consequence of two trends," said Andrew Arthur, report author and vice president at MRI, in a statement. "[There has been] a steepening decline since 2000 in the percentage of households with any landline, accompanied by a rapid rise in the number of households with at least one mobile phone."

"The MRI data show that 84.5% of people now have now have landlines in their households," Mr. Arthur said, "while 86.2% now have at least one mobile phone."

MRI conducted its study from September 2006 to April 2007.

Mobile-only households skew young, and with good reason, according to MRI.

"Logic would suggest that single-person households have less need for a landline," Mr. Arthur said. "And, of course, fewer income-earners to pay for one. More than one-half of 18-to-24-year-olds who live in single-person households are now mobile-only, making them more than four times as likely to be mobile-only as the average adult."