is there a limit of data that can be used on umlimited data plan?
From what I have read, you will want to keep your usage < 100GB per month.
So technically, no it is no longer "unlimited", however if you use 20-30GB per month it can still end up being a really good deal compared to current plans (depending how many minutes/texts you have on your account).
If your usage is only a few GBs per month, then odds are you can likely save money by switching to one of the newer plans.
This is what some have pieced together. Verizon to disconnect unlimited data customers who use over 100GB/month | Ars Technica
And several people have reported losing UDP today. One reported usage 150-200 GB per month.