This function allows you to delete telephone numbers from a list of telephone numbers that do not want to receive calls or that should not be called for any other reason. This requires a second list, the blacklist. This list can contain entries in the following format:

• a complete telephone number
• '+850' => all telephone numbers with this country code are blocked (-> North Korea)
• '+850 2' => all telephone numbers with this area code are blocked (-> Pyongyang, North Korea)
• '+850 2 12345' => all telephone numbers beginning with the specified digits are blocked