I believe video messaging is included in the data plan (see the included features in the link below).    Yes, I also believe they are referring to the extra charges you might incur if you didn't have the data plan.

http://www.verizonwireless.com/b2c/store/controller?item=planFirst&action=viewPlanDetail&sortOption=priceSort&catId=409&typeId=5&subTypeId=13&lid=//global//plans//mobile+broadband+plan