Who called from 2123723681

I got a call from this number.  It said it was a call from AT&T and I should press 1 to join the conference call.   I hung up

Someone must have mistakenly put your number into the system, it doesn't do auto calls to random numbers.

I also got a call this morning from this number; it was exactly the same as Vicki's call on 24 March 2010.  I just hung up.

I believe this might be from an online conferencing system where an attendee inputs their phone number and then the conferencing system calls them up to connect them to the conference.  If the attendee mistypes their number the system will call an incorrect number, hence yours.  Just treat it as a mistyped phone number and hang up.

You are correct. Automated callback to the wrong #.