data plan is required. unlimited texting is in addtion to that.
You can go on Ebay to buy an unlocked one, but you have to make sure it works with AT&T (cingular) and you need to have an active service with them. If you dont have AT&T right now, and you want to buy one, you HAVE to get the data plan, along with the regular phone plan. You cant get around it and the other carriers, Verizon, Sprint and T-mobile all require the same thing.
The main target market for those phones are the business people, engineers etc... ones that need it for work.