EC500 is a licensed feature. You need to use 1 per number you want to block - so you need at least 1 EC500 license.
As for blocking it to all numbers except 1, you can do that in CORs. Each COR has a setting of whether it is allowed to call other CORs or not - so, you'd just have 1 COR that is not allowed calling any other CORs, except for a special COR and you put that special COR on the phone you want to be able to be called.