T-Mobile - No activation fees + 10% discount on no-contract plan
First of all become a member of Studentrate, it's free and open to everybody. Them, call 866.464.8662 and order your phone with the customer service rep. Over the phone mention that you are affiliated with Student Rate (which means that you are a member of the site) Use promo code 13997TMOFAV. See flyer for more information.
if you are a new T-Mobile customer, that should be it and your discount is applied.
If you are upgrading, they might ask you to prove that you are a member of the SR site (you send them a copy of your member ID which you can find in your profile), and then they will apply your discount.