FAN discounts are discounts that come from being affiliated with a company or university. These discounts can be applied to plans, various phones, and both. Unfortunately I don't think it's possible to have them applied to a personal account if you don't have any of these affiliations. If you are a student or do work for a company and have an email address, you can go to the AT&T website and check to see if you're eligible. Here is a link for a little more information, Business Discount
Follow what dave said and if you don't have an e-mail address through your place of employment or school. You can take an ID card, par stub or w-2 to an AT&T Company Owned Retail store and they will get your discount applied.
Correct that is how I got mine by submitting my las two paycheck stubs and a copy of my employer I'd.
They used to process the FAN form at the at&t stores, but not anymore, you have to fax it to this number. Tip: you can google and download the form online from their website.
After faxing it in, it should take two billing cycles for the discount to apply. I have been getting 15% for many years now. (believe I saved that form in pdf format somewhere on my HDD, if anything do a google search)