"Data" typically refers to e-mail, web browsing, etc.
"Messaging" typically refers to texting, picture and video messaging.
You have to check what kind of plan you signed up to get the real specific details. Since you have a smartphone, chances are you signed up for either
http://www.verizonwireless.com/b2c/s...d=49&catId=448
or
http://www.verizonwireless.com/b2c/s...d=50&catId=947
Most likely, latter.