Not just those who can't remember a four digit code, but how about those who never got your code? I tried to call an old friend the other night whom I hadn't spoken to in years. He's got that feature installed and I have no idea what his code is. So, I didn't get to talk to an old buddy I hadn't been in contact with in a very long time. And there's no way to leave him a message letting him know I called.
There are always technological solutions out there. Sad we have to pay to keep telemarketers from calling us.
They've done one better than that. They've passed a law allowing you to have your number listed as a number that telemarketers are not allowed to call. And when they do call, you can report it to the FTC. When they get enough complaints, they can take action against them. I've got all of my home numbers (and I have a few) listed on it. I can't even remember when was the last time I received a telemarketing call.