Block text messages?

Maybe it has been discussed before (although I searched and didn't find anything), but I am trying to figure out how to block text messages on my daughter's phone so she doesn't go over her limit! Do you have to block the whole phone number of the sender, or can you just selectively block text messages from a certain number? Thanks for info.

Update: Duh - same question asked farther down this section - but it didn't show up when I searched! Question answered!