All smartphones on Verizon require the $30 data plan. The "dumb" phones are optional, but from my own personal teenage opsy I'd say block all data if you don't intend on using it.
For my Blackberry, i'm using the data plan right now so I'd say it's pretty important
For work, I use the blackberry version of Footprints Nomara. It's nice to close out requests on the go without a computer.