Try activating Anonymous Call Rejection to block private or anonymous numbers. Also Call Intercept can be a useful optional feature: it screens all unknown, unavailable and private numbers and also may provide you with the ability to completely block up to 25 numbers from reaching you. I also understand that people with FIOS Digital Voice already have the ability to block up to 10 phone numbers. From what I understand this can be done by logging in to your online account and following the on-screen instructions. On my phone service Anonymous Call Rejection is activated simply by dialing *77, but it may be different for people with FIOS Digital Voice, I am not sure as I do not have FIOS Digital Voice.