Yes, to use a blackberry you need some form of data plan. You have different options. A 25 mb plan maybe enough for you depending upon your usage.
A lot of people seem to have trouble swallowing the cost of a data plan especially if its the first time they have considered it.
In my opinion, they don't know what they are missing. For me having the browser at my fingertips changes the way I live.
The blackberry is a great platform with solid apps, messaging and organizing features.
If you can get past the sticker shock, the maturity, stability, and usefulness of blackberry is worth the switch.