Caller ID "Unknown Number"

[BugmenotAccount]

I keep getting telemarketers calling me and on my caller ID it says "Unknown Number". I want to call them back and say "put me on your do not call list". I've already registered on the national do not call registry but it isn't helping.

Does anybody know how I can figure out this "unknown number" or what is the code to call somebody back?

[Griffinaz]

I know on home phones you have the ability to block unknown numbers. You might ask AT&T and see if they provide the ability to block those types of calls. On a home number the caller receives a message that they must press *82 before the number they are calling. This 'forces' the system to display their number to the person called.