Over 20 million US telephone households (17 percent) are now "wireless substitutors" — homes without landlines that rely solely on a mobile phone — and one in five households could be wireless-only by year's end, according to a study by Nielsen Mobile, writes MarketingCharts.

As the US economy tightens and consumers seek ways to cut household spend, many are choosing to eliminate their landline phone service, which costs an average of $40/month per landline household, Nielsen said.

Specific stats about cord-cutters, according to the Nielsen Mobile study (pdf):

• US cord-cutters tend to have lower income levels: 59 percent have annual household incomes of $40K or less.
• Smaller households, with just one or two residents, are more likely to cut the cord than larger households.
• Moving and changing jobs are the biggest life events associated with cord-cutting.

• 31 percent of cord-cutters moved prior to cord-cutting, and 22 percent changed jobs.
• Wireless substitutors tend to use their mobile phones 45 percent more per phone than their landline peers, but still save an average $33 per month in a household of one subscriber, less $6.69 for each additional wireless resident.

"As wireless network quality improves and unlimited calling becomes increasingly pervasive, we expect the trend toward wireless substitution to continue," said Alison LeBreton, VP of client services for Nielsen Mobile. "In a tightening economy every dollar counts, and consumers are more and more comfortable with the idea of ditching their landline connection."

Wireless substitution doesn't work for everyone, however: 10 percent of landline phone customers have experimented with wireless-only in their household, but then returned to landline service, Nielsen said. The primary reason people re-establish landlines is because they need them for other services, such as security systems, satellite TVs, pay-per-view services, and fax machines, among others.