jlf: I think att allows you to do that
relevant quote: "Most mobile companies do, in fact, allow customers to turn off text messaging on their accounts, although some make it easier than others. AT&T, for example, offers it as a simple radio button on its website in the section that allows customers to add or remove features, which is fairly easy to find. (We confirmed with an AT&T spokesperson that this was the right way to turn off text messaging on one's account.) "