More and more U.S. consumers are using only mobile phones, partly due to the slower economy, according to a new Nielsen study.

Nielsen said that 20 million households, representing about 17 percent of the country, rely solely on a mobile phone for their communications needs. The number could go up to 20 percent of all New York-based homes by the end of 2008, Media Post reported.

The study also noted that the average monthly land-line phone bill is $40. Those who switch to mobile-only are mostly at a lower level of household income - almost 60 percent have $40,000 or less annually. It also found that households consisting of just one or two people are more likely to be mobile-only.

The biggest impetus to cut the landline cord is moving or changing jobs: 31 percent of cord-cutters moved prior to cord cutting and 22 percent changed jobs, according to Media Post.

Wireless-only consumers tend to save $33 on average a month, and use mobile phones 45 percent more then those who still keep landlines. However, the study noted mobile-only is not suitable for everyone. Ten percent of phone customers who have experimented with wireless-only in their household eventually go back to keep a landline, Media Post reported.