Here are the steps to unlock your SIM card on the iPhone.
Contact the Carrier. You need to contact your carrier straightaway. Since you're locked out of the iPhone, you need to make a call through another device. If your carrier has a website, opt for customer service via live chat to unlock your SIM card.
Get PUK Code to unlock. When you talk to your carrier customer service for a SIM card-locked iPhone, ask for the PUK code. Once you obtain it, input it in the "Enter PUK" option. If you cannot see this option, go to settings and then to Cellular. If you cannot see this option, then reboot your device. Remember that the PUK code is 8 digits long, and you will get only 10 attempts to be successful. Make sure you have it correct on the first try only.
If you're still out of luck after contacting the carrier customer service, then you can try a 3rd party tool (such as iMyFone's iBypasser) to remove the SIM card lock and other activation features. Though you may not be able to make calls or use cellular data until your SIM card is processed, you can usually use other functions.
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If you want to unlock your iPhone from the sim lock, use a remote unlocking service.