In the devices settings page there is an option for "Can send & receive picture & video messages". The fact that it is under the "Messages" section is misleading. It should be under the "Megabytes" section. Where it is located now suggests that you can use this feature and it will only count against your text messaging charges. This is NOT true. By sending photo messages you are using Megabytes from the data plan. In reality sending a photo message uses both text messaging and data, but if you were going to choose just one section to list that option under, I would choose the Megabytes section. It would also be helpful if this fact was documented somewhere and didn't have to be found out by talking with tech support. Most people would assume photo messaging doesn't use data because that is how it is on most (all?) other carriers.
Move "Can send & receive picture & video messages" under "Megabytes" section