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Insert your new SIM card in your new iPhone (if necessary). Power on your new iPhone. Slide the "Hello" screen to start the setup process. Select a wireless network. Wait for your iPhone to activate. Proceed with your iPhone's setup.
Your new iPhone will come with a SIM card if your carrier requires one. The SIM card may already be inserted in your phone. Not all carriers use SIM cards. The SIM tray can be found on the right side of the iPhone. Use the SIM removal tool or a small paperclip to eject the tray. New phones will take a few moments to boot up. If you are trying to activate a used iPhone, you may be prompted to log in with the previous owner's Apple ID. The only way to bypass this is to perform a complete wipe and reset of the iPhone. If this still doesn't work, the previous owner reported the iPhone as stolen and it cannot be activated. Enter in the password if the network is secured. If you don't have access to a wireless network, you can plug your iPhone into your computer and use iTunes to activate the device. You will be prompted to activate automatically after plugging the phone in. Your iPhone will attempt to activate automatically as soon as it connects to the wireless network.  If you receive a SIM card error, ensure that you have the correct SIM card inserted in the iPhone. If your iPhone can't connect to the wireless network, plug it into your computer and use iTunes to activate the iPhone. After activating, the setup assistant will continue guiding you through the iPhone's setup process.