I bought a sim card that was identified to be specifically for the iphone 4s. I put it in my phone and at first it siad 4g then when I called At&T to have them fix a bill error it automatically dissappeared. Is it ture that all sim cards only work on the 3g network reguardless of series on phones? I only purchased an unlocked phone thinking it would save me money and free me of phone companies grip but it seems as if I end up paying more. Input would be appreciated. ME