I talked my brother into upgrading his phone to the Blackberry Curve. He has no interest in the data plan to use any Blackberry features. He just wanted to text and talk on the phone. After a day he called me and asked why he can't set up an e-mail or go online or download anything fun. Right away he added the data plan after I told him he needed it to do any of that stuff. He claims that it just needed to be added on to his Sprint unlimited everything plan but I'm sure he's paying extra each month for it.
Many great answer here, myself I would go with unlimited data (30 buck a month) also have unlimited text on three phones (15 bucks a month), I have a teenager who doesn't know to function w/o texting.