In some cases, the only thing you need to unlock your phone is a software update your carrier will push to your device, and then you insert the new carrier’s SIM card and you’re good to go.

How to update an unlocked phone without the SIM card If you’ve requested an unlock from your carrier, but have not got the original SIM card, or if you have acquired a locked iPhone from someone ...

(Subscriber Identity Module lock) A function in GSM cellphones that restricts the phone's use to a particular cellular carrier identified by a SIM card. SIM locks are used to ensure subscribers ...

You may find that you need to check the cellular service carrier of your iPhone, especially if you are planning to follow carrier requirements to unlock it ... doesn't have a SIM card, you won ...