Wrong - we recently upgraded a phone and ended up in a big fight with Verizon. When we upgraded the phone in the store we made the rep swear on a stack of bibles that the unlimited plan would not be terminated. We even made him bring over his manager.
Next month we get bill with $100 of overages and find we are now on a 2GB plan for same price as old unlimited plan. Of course we screamed. Store was locked out of computer for making changes. So we spent about two weeks harassing them over the phone. Finally when we brought in all three phones we had back to the store and told them to compute the early termination charges did they start talking.
They ended up giving us 6GB for the same price we were paying for unlimited previously and took off the $100 overage. We are still not happy about this and will definitely be shopping vendors when contract expires.
So it is not clear to me if there is a solution to keeping the unlimited plan. We were ready to terminated our entire 10 year relationship with Verizon and still they wouldn't give it back. Now they have just deferred things for two years and we will definitely be shopping then.