We have what's called naked DSL or dry-loop (it's de-coupled from phone service). At least in my market, the phone company's system still uses phone numbers for everything so there is a phone number for the account but it doesn't function and you can't plug a phone into it. The FCC has mandated it as a concession during large mergers, so it's available pretty much everywhere in the country.

According to the CDC, as of June 2010 about 25% of US households have no wireline phone but have at least one mobile phone.

http://www.cdc.gov/nchs/data/nhsr/nhsr039.pdf

This comes up every election year because of the prevalence of phone based opinion polling. Younger people are more likely to not have a land line and thus not be polled, etc etc.