iPhone Won't Register
Diagnosing the reason behind an iPhone registration problem provides you with the information necessary to find a suitable resolution. Hardware issues can prevent your computer from recognizing your iPhone. Software-related problems could result when a previous owner does not properly release the device. A lack of network connectivity could prevent the device from connecting to the registration server.
1 Hardware Issues
The SIM card provided by your carrier stores information about your service provider. In some cases, you may need to request a new SIM card or replace the current card if the card suffers damage. Usually, you visit your carrier to have a faulty SIM card replaced. However, before seeking assistance from your carrier, reseat the SIM card to see if that fixes the problem. This usually solves the problem when a previously registered iPhone displays a message about a missing SIM card or an activation issue. You can use the end of a paperclip to open the SIM-card tray. Power off the iPhone, locate the small pinhole on the side of your device and press in gently with the end of a paperclip. Remove the SIM card and replace it to reseat the card. Turn on your iPhone and attempt to register it again.
2 Network Issues
You need a solid network connection to register the phone. Test the connection using your computer or try connecting to another network to see if that resolves the problem. Connect your device directly to your computer and register your iPhone using iTunes if you can't connect to Wi-Fi on the iPhone. If that doesn't work, restore the iPhone. On the phone, tap the "Settings" app, select "General" and choose "Reset." Select "Erase All Content and Settings" and attempt to register your iPhone again. This option deletes all your information and data, so create a backup before you restore to preserve your data.
3 Previous Owners
When you buy an iPhone from a private seller, ask the previous owner to unregister the device by logging in to his support profile on the Apple Support website (link in Resources). If the iPhone displays in the My Products section, he needs to remove it from the list of products before you can register the device. After the previous owner deletes the device, attempt to it register again.
4 Disable Activation Lock
You might need to enter the previous owner's information into your iPhone when attempting to activate a device with Activation Lock enabled. This prevents unauthorized users from using a stolen iPhone. If the previous owner can physically access your iPhone, ask her to enter the Apple ID and password associated with her account on the Activate iPhone screen. After she removes the device from her account, you can register the device with your own information. Instruct the previous owner to access the iCloud website (link in Resources). Ask her to select the "Find My iPhone" icon, click "All Devices" to show a list of her registered devices, and then select the "Remove From Account" option for your iPhone.
Information in this article applies to iOS 7 and iTunes 11. It may vary slightly or significantly with other versions or products.