Your SIM card, or subscriber identity module, allows your iPhone to be uniquely identified by the cellular network and allows you to receive calls made to your phone number. Installing the SIM card on an iPhone is easy, but the procedure is not obvious at first. The SIM port is located on the outer edge of the phone, but requires a special or homemade tool to access it.
Bend out one end of the paper clip so that it points out.
Locate the small hole along the edge of your iPhone. This hole is on the middle-right edge of an iPhone 4 or the middle-top edge of an iPhone 3GS. Push the pointed end of the paperclip into this hole until the small SIM tray pops out from the iPhone next to the hole.
Pull the SIM tray completely out of the iPhone.
Lay the SIM card into the SIM holder with the notched corner along the top-left corner of the SIM holder, or against the left side of the SIM tray's exposed end, which lies flush along the side of the iPhone.
Push the SIM tray back into the SIM slot until it locks in place.
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