Looking at this from the, shall we say, shadier side of the fence, there are a couple of ways that you can sign a 2 yr contract, get the subsidised pricing and still keep unlimited data.

However, all of these options involve signing contracts on different lines than the one with unlimited data. The two most common ways that i've seen in the indirect channel is either us a different upgrade on the account or start up a new line, get the new phone, put it on the old line and have an old flip phone or a Test Device esn on the new line. From what i understand, these methods are frowned apon from the Verizon peeps that be, but they exist.

Additionally, i've seen some interesting contract manipulation done with iPads, month to month contracts and sim swapping.