It is not guaranteed but it might work. Try it at your own risk. I think it's fairly easy if you're going to be New AT&T customer. Generally, for registering discount, AT&T sends you a link at your work email and when you click on that link it shows you how much discount you can get and that's all you need for verification !!!

Here's how you can get to that link without having a work email address.
Let's say you want to get discount what McDonald's corporate employees get, Follow the following steps.
(1) Go to www.att.com/wireless/mcdonalds
(2) Enter zip code
You're now logged in as McDonald's Corporate Discount website and you can order phone with Discount. You can see eligible discount when you click on Discount Registration tab.

McDonalds gives 18% service discount i believe.

If you really want maximum employee discount (30% off monthly , includes data plan !!)) then go to:
www.att.com/wireless/timewarner

Again, I am not sure if AT&T will verify after you order it because even after clicking on your legitimate work email address you get to the same point with above tricks !!!

Do it at your own Risk !
Enjoy !