Unfortunately Jessica, a datablock also prevents pictures messages (MMS) because that, although free in itself, needs data enabled to work :(
Your only option is to have the datablock disabled I'm afraid... or stick with SMS messages only.
Keep in mind even though you need data to send picture messages you do not get charged for it, but it can be hard not to get charged for data other usages while having data enable on your phone just to specifically send pictures.
I usually suggest to clients that they can turn the data off in the phone. Turn it on when you want to receive or send a picture message. I know it can be annoying but at least your not getting accidental data charges.