Is T-Mobile's unlimited plan only for a "limited time"?

I was reading through T-Mobile's website and their various plans. One thing that caught my eye in particular was the following fine print:

Limited time offer; subject to change. - Individual plans page

Do you think T-Mobile is trying to pull a fast-one with their "uncarrier" campaign or is this just some legalese that they're required to include?

For reference, I came across this fine print by getting into a conversation with a Verizon rep on Twitter. Is VZW just desperate to keep my business? Here's the thread for anyone interested:

What are your thoughts?