I I applied for a job from craigslist and received a call from this number under the guise that she was an AT&T Representative for a job in Rochester, NY. She asked some what seemed normal job questions and then for my social security number for a background check for AT&T

I also received a call from this number.  I'm already over my minutes and I see a voice mail icon on my cell phone. I have to get rid of it, but don't want to exceed my minutes even more... pffft!!!  Anyone who asks for your social security number...especially over the phone in all.... is FAKE. Scam. Because.... Uhh... it says it right there...."AT&T Rep and the job is in NY????" Uh... ok. Anyway.... sounds like a scam.

I am the manager of the recruiters you speak of that have contacted you.  I can assure you this is no scam.  AT&T requires an SSN prior to submitting candidates to any open job order within their national system.  Here is wording from a letter we typically provide to our candidates from AT&T:

"AT&T eCAM Preferred Vendor:

eTEMP (Temporary Engagement & Management Program) is a web-enabled system which automates the contractor requisitioning and recruiting process. It is owned and supported by the Enterprise Contractor Acquisition and Management (eCAM) group. Social security numbers for each submitted candidate are required to be input into eTEMP for tracking purposes.  There are no exceptions to this requirement.  

The social security numbers provided for all candidates are kept confidential and secure within the eCAM organization and are not released to other areas of AT&T or outside the company."

We understand this isn't the norm, but its something we deal with regulary.  I hope this helps to quel some of the fears and reservations you may have.  I think you are right to be cautious with your SSN and should always ask for backup documentation or another way to contact the recruiter to verify their validity before surrending this type of information.