I decided to buy my iPhone 4S on ebay and I have received it today. The phone was brand new and sealed, when I tried to insert my UK 3 sim card to activate it, it shows this message: Only compatible SIM cards from a supported carrier may be used to activate iPhone. Please insert SIM card that came with your iPhone or visit a supported carrier's store to receive a replacement SIM card. The seller said it was unlocked, does this mean it is locked to a network? Or will I need the seller to activate it with his sim card and then I can use any network?