Here's a proposal on how to implement blacklist/whitelist in PhoneLeash (prompted by metsox's question, as well as another user a nurse dispatcher).
Right now, PhoneLeash only has a blacklist. You can use the "block nnnn" command multiple times to block notifications and SMS from these numbers. Everything else gets through. [To unblock use the same command, its a toggle.]
What metsox wants is a whitelist. Block everything by default, only allow some numbers throug. So I am thinking of an "allow nnnn" command. Simple enough.
In order to retain simplicity and avoid a forest of setup screens, I believe blacklist (block) and whitelist (allow) are EXCLUSIVE. You are in one mode or other, not both at the same time. Does this make sense?
( no friends, help! ;-) )