Need to change passcode when calling

I received an email asking me to change my 4 digit passcode. Whenever we call or go into ATT we always have to give our last 4 digits of our S.S. # but they want to change that now and have people come up with a 4 digit code.

Does this email sound legit? It looked legit. I'm freaking out a little bit. Don't know if it's a "phishing" scheme! HELP-anyone know about this?!