http://support.verizonwireless.com/clc/devices/knowledge_base.html?id=20989
LOL at AT&T not blocking. I can go on the Sprint website and block over 100 numbers indefinitely.
Edit: Nevermind about my AT&T jab:
http://www.att.com/esupport/article.jsp?sid=KB102428&cv=820#fbid=fz3k_bJo4dG
Oh wait, you have to pay $5/month. Nice one, AT&T.