You go right ahead and "report" the 10-12 calls per day I get from numbers that DO SHOW CALLER ID, but they are FORGED! If you dial them back, you hear a recording saying they are not a working number. They come from a computer somewhere half-way around the world and insert a phone number with software from a list complited by more software to find disconnected numbers. They are UNTRACEABLE and the government: FCC, etc. cannot trace them. AT&T or any other carrier, could use a quick 'handshaking' routine like that used by ALL EMAIL servers, to be sure a call is from a real number before connecting it to my phone, but they are TOO GREEDY to allow the tiny bit of bandwidth to do something they USED TO DO.
Furthermore, these calls play a recording, they don't have a human at the other end. The recording is a sales pitch that fills up my voicemail every day, because I've chosen "block number" on the little apple "i" with the circle in the call log. This IS something the iPhone software could control, if Apple wanted to. But the carriers want this traffic, so they can sell $5/month add-on cost to block 30 calls you must continually update.
AT&T will do nothing. NOBODY ELSE CAN do anything, because the IP address of that CRIMINAL phone call (all calls made by machines are now illegal if a human isn't there when you answer) is only known to AT&T if they look in their cache before it disappears, usually 24hrs or less.
Oh, and since you are giving completely uninformed advice, why don't you do like AT&T and tell people to get on the Do Not Call List, because you KNOW those criminals respect THAT when they get their FREE COPY from the US Government of GOOD WORKING NUMBERS who don't want to be called!!!!!!!
I don't want to change my number, but don't know how to stop these stupid "lower your student loan" calls. I know AT&T could stop these criminals, if they wanted to. But they are criminals, themselves, and made Congress pass a law exempting them from class-action lawsuit. How corrupt is that?