Do you own a Windows Phone that's connected on a AT&T account? You might not be aware of this, but you can restrict the use of personal data, should you have any privacy concerns or simply do not wish for the carrier to contact you. Customer Proprietary Network Information (or CPNI) is personal information obtained by the telecommunications company through providing a service to the customer.
So what is this all about, and should you be bothered? AT&T collects information from you based on the services you have on your account. All carriers (and many companies) carry out the same actions to offer similar services / products to customers. If you've received a call from a company you use often who are attempting to sell you a related product, this is exactly what we're talking about.
To keep everything in check and restrict AT&T's use of your CPNI, be sure to give the carrier a call. Should you feel the need to do so with any other company, you can also enquire to request exclusion from future marketing and promotional offers where possible.
Source: AT&T; Thanks EasyPeasyJD for the tip!