I was able to get AT&T FAN account simply telling them I am a costco member.
Here are the discount for member:
Most university 10%
(You can only pick one)
Here is what my friends and I did.
Walk in AT&T and tell them I am a Costco member and would like to receive discount. They will ask you to show him or her your Costco card.
My friends and I went to
Palo Alto AT&T, the one next to Fry's (California)
Another friend of mine went to
Milpitas AT&T, CA
Including me, five persons successfully enrolled in the FAN account and receiving 15%. (not sure is it California only)