Prevent to call to restricted phone numbers/prefixes. Restrict to call to allow list phone numbers/prefixes only. Intercept and redirect calls to pre-programmed number | Telephone line powered, no need extra power supply or battery. | Easy to install and program. Users can program it locally using a standard touch tone phone. Also, it can be programmed remotely. | Compatible with any regular telephone lines, VoIP landlines, analog PABX/KSU extension lines. Compatible with corded landline phones, cordless phones. | The programming would retain even if the call blocker is disconnected from phone line.