Check before inserting a card
Confirm the phone's exact model, supported service and carrier-lock status. Use the provider's compatibility tool. The SIM must be intended for that service and device type; a phone SIM is not automatically permitted in a router.
Power and tray instructions differ by device. Use the correct tray tool and card size. Do not force a tray or cut a card to fit. Follow the manufacturer's instructions if the device does not have a removable SIM tray.
Activate and test separately
Inserting a card and activating a line are separate steps. Follow the provider's authenticated process, using Wi-Fi if required. When retaining a number, keep the previous service active while the receiving provider handles the transfer.
Test outgoing and incoming calls, an ordinary SMS and mobile data with Wi-Fi temporarily off. Check voicemail and any Wi-Fi-calling configuration. Restore your normal connection settings after testing.
Replacement and security
A replacement SIM changes the credential used to access the subscription. Obtain it through the provider's official process. Unexpected loss of service combined with account alerts warrants prompt contact through a known provider channel.
A SIM PIN protects access to the card, while an account password protects the customer account; they are not the same. Repeatedly guessing a SIM PIN can lock the card. Ask the provider for the correct recovery procedure instead of trying codes found online.