I have now seen all of the following, none of which have been publicly stated by Verizon:
1) You will lose unlimited data and will be forced to pick a new plan when you switch phones. This will definitely be true if you buy a new phone online. If you call customer service, they should be able to manually grandfather your replacement phone.
My thoughts: I could see this happening online, based on Verizon's website always requiring you to pick a plan everytime you purchase a new phone. They always walk you through what you have, and have you choose the most current options if what you have is no longer current.
2) Your unlimited data will expire at the end of your contract term, at which point you will have to pick a new data plan.
My thought: Also possible. Although I have never seen a carrier do this, but anything is possible I suppose.
3) The Bionic will be your last shot at an Unlimited data package so you better get one now.
My question:? Why the Bionic?
4) Today, March 24th, is the last day for unlimited data as reported in a forum.
My thoughts: I think Wall Street, and the blogs/media will get a hold of this news before a forum does, and I think there will be more than a days notice. Also, the TB has only been out for a week now. Their network is very robust. They are not freaking out at our level of consumption. The purpose of tiered plans will be to make more money. They first need to gather some info about how we are using our phones and how much data they are utilizing. It will take some time before they figure out what these plans should look like and what the tiers should be. If they set them too high they will not be able to lure more users. If they are too low they won't make money. All they need to do is make $5 to $20 worth of more ARPU to satisfy their shareholders. They just don't have enough historical info to do this yet.
I also think competition will either eliminate these tiers, as it did with 3G tiered plans, or they will be fair enough that they will be designed to just keep abusive bandwidth hogging users from impacting the rest of us. That said, tier's have been and probably will continue to be enforced in Europe and most other countries. Customers eventually accept and adapt.
All speculation on my part. What I do know is just like the TB release, I take everything I read with a grain of salt until I hear a press release.