That's not true. they have ways of knowing if you tether, even if you only use 3KB. And its not true that they can't say anything at all...if you're a verizon costumer, you have signed a service agreement that says you won't tether without paying for their tethering plan. They have already said that pretty soon they will be automatically cancelling unlimited data for people who tethering without paying for it. They will put you on a tiered plan and charge you for the tethering plan at all. As soon as they implement that, a lot of people will be in trouble.
If you want to risk it that's your choice, but please don't tell other people that they can do it without consequence.