I have a 3GS that is bought on release day last year and my upgrade date is 2/11/11, I am on a secondary line. My wife got her 3GS in March 2010 and her upgrade is 3/27/11. I just called ATT and they switched my number to the primary number and told me it would take effect on June 11th when my billing cycle reset. So in theory, on June 11th, shouldn't my upgrade date switch to June 2010?