I have an iPhone 3GS 32GB. I have just tried updating the phone using iTunes. The phone is second hand, and was unlocked when I bought it. I didn't know that when you try to update it, it loses everything. Now it isn't reading my SIM, even though I've used this same SIM in the phone before I tried updating it. Now, when I turn the phone on, it comes up with:
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 does this mean? And how can I get my phone working again?