On a stock iPhone, not unless you call up your carrier and ask them to block it on their end. On a jailbroken device, you can use apps like iBlacklist that'll basically intercept any texts or voicemails. If you want to read/listen to them, simply open the app and do so. They won't show up on your Message.app, your phone won't ring if they call, and you won't see their voicemails in the Phone.app.