There are two things wrong with this.
1) If a company deliberately quotes you a price, even if they accidentally quote you too low, they are obligated to honor their quote. It was their mistake, they have to pay for it.
2) He had no idea what minutes should cost. His US plan is "unlimited", meaning he's never actually paid for a minute by minute basis. He figured that the low foreign rate was a component of his expensive "unlimited" plan. He even called to verify with Verizon that the correct rate was .002 cents per minute. They not only quoted him the wrong price originally, but they then verified it.
There is nothing about this situation that is not Verizon's fault.