If you have unlimited data now and upgrade to an LTE device at the two year contract price, you can keep your unlimited data. At some point this summer that option will be eliminated.
You will be able to keep your unlimited data plan indefinitely as long as you either a.) remain with your current device or b.) purchase your future devices at full retail price.
You will be able to keep your unlimited data plan indefinitely as long as you either a.) remain with your current device or b.) purchase your future devices at full retail price.