A subscriber identity module, or SIM, card is used to store information on mobile phones. If you have recently replaced the SIM card on your iPhone, you will want to retrieve your contact information from your old card. These contacts can be added to your new SIM card with the aid of your iTunes account. When you connect the iPhone to your computer, iTunes automatically backs up the contact information on your SIM card.
Plug the USB data cable into the USB port on the bottom of the iPhone. Connect the other end of the cable into any USB port on the computer. iTunes will launch automatically.
Select your iPhone from "My Devices" on the left side of the screen. Because you have a new SIM card in the phone, the computer asks if you have a new device or old device connected. Select "Old" devices and click on your phone number.
Select "Sync" and all of your old contacts are placed onto the new SIM card.
Click the eject icon next to your phone under "My Devices." From here, the phone disconnects from iTunes and you can remove it from your computer.