A free app for Android, by LiteWhite.

This Call blocking app is specifically made for blacklist-based blocking of phone numbers. You can use the blacklist to exclude a number or even block restricted or private calls with unknown caller ID.

Additional features include using an area code, prefix, or suffix to lock incoming calls. You can also lock caller ids from people who aren’t on your contact list, block one contact or a number of contacts and put a stop to all incoming calls. This is a free download for a number blocking program which you can turn off or on call blocking feature anytime you want.