No. Basically you sign a new contract when you get a phone so if the terms change then you accept those terms.
I think I have a way around this!
I have my primary line, that I have been doing 2 year contracts on. Got my DroidX in October on that line. Contract has unlimited data @ the 29.99 price.
I have a second line that I use for upgrades with 1 year contracts. I currently have an old dumb phone activated on that line that my Dad uses from time to time.
What I think I can do is upgrade the second line, then immediately move that phone to my primary line, and put the dumb phone back on. This way I wouldn't have to change my primary line contract!
Think that is workable? All signs indicate I may not have to do this, but its a plan...