I guess my question was about the situation when the person (me) has a 4g phone, but no 4g yet available. Will they switch me from the unlimited data plan when 4g appears locally?
From what I understand, you're looking for an easy answer that's straight forward and simple.
So here goes:
You already have a 4G enabled device, and your account is already marked for 4G service.
When you finally get 4G service local to you, your account will not change.
When will your unlimited data be changed?
That's to be determined. We know that at this point if you "renew" your contract on an upgrade, VZW will take away the unlimited data plan then. The proposed solution to this is that once our contracts are up, we proceed to just pay monthly for the same service, and if we want a new device then we need to buy it at full retail price as opposed to taking advantage of the subsidies VZW offers on new devices provided you extend your contract for another 2 years.
In the mean time though, you're still at the mercy of VZW. If they really wanted to, I'm sure they could change the terms of the contract so long as they notify you (giving you the chance to exit the contract without paying the early termination fee), or wait until your contract is up and just deny the unlimited data service.