Do you mean starting your second year or ending your second year with it. If ending the upgrade wlil be one third the discount on the iPhone (Which i believe is 500/36 *12) which is $16. If you are starting year two then it is $332. Then you pay the two year price of the S4 which is $200. The you add tax so it would be at least $400 for you to upgrade to the S4 assuming you are endign year two and starting year three and Almost $600 to upgrade if you are just starting year two.