If you data block your number through Verizon, then you will not be able to get on the internet without Wifi and therefore will not be charged for data access. However, you will also not be able to send or receive picture or video messages.
Not true. You can request a data block but allow MMS messages (pics and vids). I've done this. If they're part of a text/pix/vids package, they don't fall under data usage.
I go some very good advice from the Verizon sales rep on the phone. He shut off access to 3G at his end, to prevent accidental charges for data or msg via 3G. He said I should go into Settings, and turn on the WiFi WHEN I want it (and another forum also suggested I turn on the Airplane Mode, to be sure the 3G doesn't kick in--you can see it gets x'd out on the "dashboard" -- if you tap on the date on the lower right corner of the screen and the WiFi symbol becomes dark black when it's available). And remember to put back both OFF when done. (Turning OFF the WiFi when you don't need it helps to save the battery and prevent accidental switching to 3G.
It's a little confusing, but I'm getting the hang of it.
It seems pretty bullet-proof, the way you are doing it. Both turning on airplane mode, as well as blocking data on Verizon's end will successfully block the data, making sure you don't get charged. You shouldn't need both, but i suppose if you're already doing it, it doesn't hurt. One more way to block data is through the phone's hidden programming menu. From there, you can block all data connections to and from the phone, but the downside of doing it this way is you can't send/recieve MMS either. The downside of airplane mode is it also disables the phone service of your phone, meaning you can't call or text, incoming or recieving, when in this mode. It essentially is a temporary way of disabling all network connections from the phone, and like its name says, it was originally designed for disabling the phone while on flights, but still being able to access other parts of the phone. I can't really think of any downsides of blocking data through Verizon, since you get everything that you do when you block data from the phone, but if you do it correctly, you can successfully keep MMS functional. True, turning wifi off when not using it will drastically save battery, and i highly recommend it.