If you RTFM, it tells you how to do this.  However, if you call me,
you'll get VM.  I don't respond to callers that hide from me.

yes it is possible.  Let me get the info for you, so watch future posts.

blocking caller ID...

https://www.wireless.att.com/support/tutorials.do?tutorialPage=page2&universe=ci
ngular&deviceId=7410&tutorialsCategory=Voice&tutorialId=126050

Beware.  I have outbound number blocking on one of my business lines, and I
once called a number that was a Cingular Wireless line.  The wireless
subscriber was not on network, and the call went to voicemail.

I was given the option of pressing "5" to page him, or of just holding on to
leave a message.  I pressed "5" and a recording came on that read off my
"blocked" phone number, and asked if I wanted to send that callback number
to the recipient ("Press 1 if correct or 2 to send another callback number .
. . ")

So much for number blocking.  It turns out that you may be able to block the
recipient from seeing your number on his display, but your number IS
transmitted to the wireless carrier, and they are able to keep a record of
it.  I suppose that they would be able to release it to criminal or Homeland
Security authorities if such a request were made.

Blocking your outbound number is not as airtight as one might assume.