I have just implemented a whitelist on my phone system. Those of you who are in my address book should notice no change, however those of you who are not will have to step through a hoop to get the call connected. I will say no more than that, but it’s a relatively painless one-time process in order to add another layer of convenience and privacy to my phone system.
Why is Whitelisting Absent from Telephones? :: TechMiso.