I've not seen any ads that advertise unlimited gigabytes.
Verizon has/had a plan simply called "Unlimited Access" that they sold in New York State. They didn't specifically use any terms denoting quantity ("gigabytes") or any other usage restrictions in their plan name or advertising; they left it wide open to the customer's imagination, in their advertising/marketing (although not in the actual contract), as to what "Unlimited" implied. And, they got spanked for it by New York Attorney General Andrew Cuomo back in 2007 for "deceptive marketing." Verizon agreed to stop the "deceptive marketing" and reimburse Verizon customers in New York State $1 million.
Cuomo's action was most likely brought on by vocal consumer backlash in various forums:
Apparently, at least in New York State, the contract doesn't mean much if you are judged to have engaged in deceptive advertising while trying to sell that contract.
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All my life, I always wanted to be somebody. Now I see that I should have been more specific.