According to author David Weinberger, who made the discovery upon reading his pamphlet, the personal info Verizon wants to distribute willy nilly to anyone with a check includes "services purchased (including specific calls you make and receive), billing info, technical info and location info. They promise to only share this with 'affiliates, agents and parent companies.' It will definitely not be shared with 'unrelated third parties' ... unless, perhaps that third party pays Verizon to become an affiliate, whatever the heck 'affiliate' means."
If don't get your statements in the mail, and view them online like I do, you will not receive this letter. Instead, you have to log into your Verizon Wireless account and view your messages. However, Read Write Web reports the link provided there, called the Customer Proprietary Network Information Notice, was listed as "not available."
So keep an eye out for the mail, and be sure to opt out. Or, log in and hope Verizon grants you access to your own account so you can cancel the notice that way. [Read Write Web]