After seeing this thread it got me thinking if I should try to call and get the 1 year pricing, especially since I paid $250 for a 2 year contract. Although I'm not sure if I want to give up 2 years of unlimited 4G at $30 a month.
If I understood you correctly you are under the impression that your 4G pricing is based on your contract length and can change when your contract is over. However, your unlimited 4G pricing won't change as long as you don't alter your 4G data plan. The length of the contract doesn't matter either. In a year if I decide to get a new phone, I won't be altering the data plan on my line but just upgrading the phone and retaining the $30 data plan price.
They call this being grandfathered in, which was one of my deciding factors for getting the Thunderbolt.