As a relatively new smartphone user, I am surprised that an option to accept only calls from your contact list is not a built-in option on all (any?) smartphones. We've had a "black box" for years that does this for our land line (without it, my wife and I would have been nuts by now). I realize that cell-phone users have not been subjected to the high volume of telemarketer calls as have land-line users. But this could change in the future. It doesn't take a retired rocket scientist to realize that a "blocked callers" list is of little value. What is needed is an "accept callers" list.