Power down the phone, then replace the old SIM card with a SIM from a different network. Check that the iPhone is able to connect a phone call over the new network. That’s the short version ...

Whether you need to make the change or want to leave physical SIMs ... You're probably already familiar with the SIM card, a tiny chip in your phone that connects it to your cell phone carrier ...

Whether you need to make the change or want to leave physical SIMs behind, you can likely do so with just a few steps.