The SIM card in iPad Wi-Fi + Cellular models is used for your cellular data connection. If your SIM card isn't installed or if you change carriers, you may need to install or replace the SIM card.

Open the SIM tray. Insert the SIM eject tool into the hole on the SIM tray, then press firmly and push the tool straight in until the tray pops out. Pull out the SIM tray to install or replace the SIM card. If you don't have a SIM eject tool, try the end of a small paper clip.