When you did an request for a web page on their network, Verizon would silently add an header to your request with an ID tied to your data plan contract. The point was to enable them to sell analytics services that tracked users from their network across the sites of their clients.
If they can sell you and get paid by you for the privilege, why wouldn't they? Capitalism, as a good and effective market philosophy, is built on all parties being aware of all aspects of the transaction and ideally of all transactions... a perfect market. If such a thing doesn't exist, which it does not, then it's selective fuckery. However, it tends to exhibit less fuckery than most other systems... except when it doesn't.
well, it's more like, "You may be the product even if you're paying. Who knows because nobody will tell you because they're not required to tell you." But yeah, 'you are the product' is probably the most accurate.