Blocking numbers/contacts

Take a look at this support document and see if that answers your questions. http://support.apple.com/kb/HT5845

If you remove the contact, that would probably remove the block. The only reason the block works is because it recognizes the number you have in your blocked list, and that is based on it being in your contacts. I'm not sure that it would remain blocked if the contact is removed. Then the only way to be able to block the number would be to make contact with your carrier and see if they provide call blocking services.

Generally device manufacturers do not handle call blocking. True call blocking comes from the carrier. The call block on the iPhone works when the correct instructions are followed. Just leave the number on the device, or have the carrier block it.