Earlier this year I purchased a used, refurbished and 100% unlocked iPhone 4s. I took my T-mobile SIM card out of my old phone, put it in the 4S and it worked right away.

Tonight I tried to go to Cricket to switch (for the $100 rebate) and the girl behind the counter said the phone would not work with Cricket.

I've contacted the seller of the phone, but as that was 6 months ago, I doubt they'll do anything.

Any ideas of what I could try?