This reminds me of when I got my Treo 650. When it came out, they told "us" we "had" to have the $39.99 data plan. Every store you called would tell you the same thing. I told them I hardly used data, with crossed-fingers, and fortunately got the cheaper $19.99 data plan. Some had to change their plans online, others were able to get them changed in stores. The bottom line was that you had unlimited data with the $19.99 plan. I believe others were able to access Exchange servers while doing that on the cheaper plans.
Sometimes, they really try to steer you into getting the more expensive plan
I'm going to try to avoid it again.
Personally, I don't think it's worth it.