No, there's a plan access fee (for example, on 1GB plan - $50, 2GB - $60. etc), plus line access fees ($30 for basic phones, $40 for smartphones). The discount will be on the plan access fee. I think you might be calling the plan access fee the data charge.
Actually, I'm pulling all of this directly from my VZW training material. We're all talking about the same thing, we're just calling it by different names. So to use your terms, the discount will apply to the data charge.