If you are an owner of the iPhone 4 and have upgraded from the iPhone 3GS, you may find it complicated to open the micro SIM card slot. This is because the area where the slot is located is made completely of metal, whereas that of the 3GS was plastic. However, with some resourcefulness, you can quickly open the slot so that you can access your SIM card.
Locate the micro SIM card slot on your iPhone. You can easily spot this on the right side of the phone in the metal back and side plating.
Find a paper clip. Twist it so that it is unfolded at one end. Gently insert the tip into the tiny hole at the top of your iPhone 4's micro SIM card slot. It will then pop out just slightly.
Gently pull the slot out using your thumb and forefinger. You will then be able to slide your SIM card into the iPhone 4 and replace the slot.