Unless you are in a two party state, in which case you’d technically be breaking CA wiretap laws, and any information you glean from the call won’t be admissible as evidence in a court. I believe that’s the case, anyway, as I am not a lawyer.
This earlier thread may be of interest to you: http://boards.straightdope.com/sdmb/showthread.php?t=448984&highlight=telephone+recording
ETA: FWIW, If you tell AT&T you are recording the call (in spite of THEM recording the call) they will tell you they will not help you and you are not allowed to record the call. And if you want to transact business with them, without the call being recorded, they will have a “manager” (read: escalation queue rep) call you back within 24 hours to transact the call without AT&T recording it.