Hello. Open your phone's dialer and type in ##77647266488 (I think it's ##programming), then Call. Type in six zeros when prompted for a code. Look for the network menu and you will see an option to turn off data. This blocks all 3G data,but you can use Wi-Fi. I believe this will also block MMS messages though, even if you have a text/pix/vids package. When finished in the menus, simply close the dialer.
SydneyK is right about the MMS blocking. I am able to recieve simple text messages, though, with the data block on the phone turned on.
The number isn't quite '#programming', i'm not quite sure what word it amounts to, but '#programmitt' will give you the right sequence of words (although i doubt that is what it actually stands for).
If you don't care about MMS, then go ahead and block data through the phone. It is the easiest and most convenient way to do it. If you do want MMS to work, You will have to block data through Verizon (online, over the phone, or in-stores); here is a link on how to do it properly (the 2nd vid, at the end) via My Verizon online:
There are various topics on these boards explaining data blocking in more detail; feel free to dealve into them and you will find your answer.
You can also block it on Verizon's site. Go into your phone's information, scroll down to change features, then scroll all the way down to service blocks, and you can simply check the box for blocking DATA only.