on my LG, I go 2
"Settings"
"Call Reject"
and from there I can add certain #'s to a "Call Reject List" and turn the "Call Reject List" ON or OFF. Pretty simple to use. What phone do you have?
I'm pretty sure you can't do it at the carrier level. There are phones out there that you can reject anyone NOT in your contacts. What you can do is save that number to your contacts, name it as like # or a . and set the ringer to off for that particular caller.