Snopes: Cell Phone Privacy

[S]ome of the privacy that cell phones provide may be eroded. Six national wireless companies (AllTel, AT&T Wireless, Cingular, Nextel, Sprint PCS, and T-Mobile) have banded together and hired Qsent, Inc. to produce a Wireless 411 service. Their goal is to pool their listings to create a comprehensive directory of cell phone customer names and phone numbers that would be made available to directory assistance providers. (In most places, telephone users can call directory assistance at 411 [for local numbers] or by dialing an area code plus 555-1212 [for out-of-area numbers] and, by providing enough information to identify an individual phone customer [usually a full name and city of residence], obtain that customer's phone number.