AT&T Privacy Manager® (a.k.a. Privacy Director)
This service works with Caller ID to intercept unknown or unidentified calls and requests that they A. record their name B. Unblock their number.  Also allows you to accept calls, reject telemarketers, or ignore calls.  This is a premium subscription which costs extra, but may be worth it if you get a lot of unwanted calls. 

To setup this service call AT&T at 1 (800) ATT-2020.

To manage your service dial:

1 (888) 575-6677 from YOUR phoneline.


Helpful Hints:

1. To manage this service, You must dial from YOUR PHONELINE. Dialing from another phoneline will simply give you a recording telling you to call back from you line (this is for security reasons).
2. When Privacy Manager® intercepts a call, your caller ID will show "PRIVACYMANAGER"  or "PRIVACYDIRECTOR" on your caller-id. This is to let you know AT&T has intercepted an unknown call.
3. This feature can NOT be used in combination with Anonymous Call Rejection (turn off ACR first).
4. Many people find this service to be expensive (it averages around 8-9 dollars monthly). It is up to you to determine if it is worth the cost. I myself, find it useful, but still grumble when paying the bill.
5. Note that if you do not answer (or an answering machine picks up) Privacy Manager® will eventually put the caller through to leave a message. 
6. This service is similar to Verizon Call Gate. If you are an Verizon customer, see here.