Other carriers, such as Sprint, T-Mobile and AT&T compile similar information to help sell ads to subscribers. As CNN notes, this is nothing new:
Selling customer information is an age-old practice that is certainly not exclusive to the wireless industry. Brian Kennish, a former DoubleClick engineer who developed the advertising network's mobile ad server, noted that wireless companies have been sharing users' location data with third parties for more than a decade.
The most interesting thing that we found was that Verizon gives third parties an incredible amount of detail on each customer, which is needed for marketing report demographics, and includes home addresses. While there's no name attached to the address, it's would become obvious with a quick public records search. And with that, you now know where all that junk mail comes from.