The SIM card is what connects your iPhone to your a cellular network.
Why Should I Remove And Reinsert The SIM Card?
Taking out the SIM card and putting it back in can give your iPhone a second chance to connect to your wireless carrier's network.
How Do I Remove And Reinsert The SIM Card?
- Use a SIM card ejector tool or small paperclip to open the SIM card tray on the right side of your iPhone.
- Close the tray once you've opened it.
- Learn more by reading this SIM card article.