This Iphone was jailbroken and used before by my brother's friend. I cut my AT&T Sim card to fit it in this Iphone 4s's tray. I inserted and waited until it brings me back to the lock-screen and says "Activation Required". It then told me to choose a wifi and so i did. Next screen shows "Activating Your Iphone", then it shows -Sim Not Valid- "Only compatible SIM cards from a supported carrier may be used to activate iPhone. Please insert the SIM card that came with your iPhone or visit a supported carrier's store to receive a replacement SIM card. " What should i do now??