If you have searched in vain for your iPhone's SIM card slot, pulled out the battery and even handed it to your 5-year-old to locate, don't worry: You are not alone. The SIM card slot is all but hidden from view, and opening requires a special tool. Luckily, this tool can be created with an ordinary paper clip. With it, you can access the SIM slot and insert your SIM card.
Straighten the paper clip out so you can access the pointed end.
Find the small hole on the right side of your iPhone 4, just about in the middle. If you have a iPhone 3GS, this hole is on the top edge.
Push the paper clip firmly into the hole to pop out the SIM tray. Pull the SIM tray all the way out of the iPhone.
Hold the SIM tray so the widest side is away from you. This is the side that aligns flush with the edge of the iPhone. Place the SIM card onto the tray with the notched corner at the top-left of the SIM tray.
Slide the SIM tray, with the SIM card on top, back into the SIM slot until it locks. Your SIM card is now installed and ready for use.
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