NEW YORK (CNNMoney) -- Your phone company knows where you live, what websites you visit, what apps you download, what videos you like to watch, and even where you are. Now, some have begun selling that valuable information to the highest bidder.
That kind of data could be very useful -- and lucrative -- to third-party companies. For instance, if a small business owner wanted to figure out the best place to open a new pet store, the owner could buy a marketing report from Verizon about a designated area. The report might reveal which city blocks get the most foot or car traffic from people whose Web browsing history reveals that they own pets.
Verizon (VZ, Fortune 500) is the first mobile provider to publicly confirm that it is actually selling information gleaned from its customers directly to businesses. But it's hardly alone in using data about its subscribers to make extra cash.
All four national carriers use aggregated customer information to help outside parties target ads to their subscribers. AT&T, Sprint and T-Mobile insist that subscriber data is never actually handed over to third-party vendors; nevertheless, they all make money on it.
AT&T's (T, Fortune 500) AdWorks program, for instance, promotes AT&T's customer base to advertisers. On its AdWorks website, AT&T touts its ability to "reach customized audience segments based on anonymous and aggregate demographics." It then shows customers carefully tailored coupons, in-app ads and Web ads.
Sprint (S, Fortune 500), like Verizon, tracks the kinds of websites a customer visits on their mobile devices as well as what applications they use, according to spokesman Jason Gertzen. Sprint uses that data to help third parties target ads to customers.