MAC Address Lock is locking your VOIP service to a particular MAC address. Every device that connects to the Internet must have a MAC address. By locking your VOIP number to a particular address, and therefore a particular device, you prevent other people from using your VOIP number to make and receive calls on your service – even if they have the credentials. This is an invaluable tool Obviously, if you need to change the device, you would have to go into the control panel a change to the new MAC address.