- You are switching to a new carrier
- If your SIM card is scratched, damaged in some other way, or otherwise not in factory condition
- To assist with troubleshooting your cellular connection
When changing the SIM card, power off the device before opening the SIM tray. After you have changed the SIM card for your iPhone you may need to reconnect it to iTunes.
iPhone keeps a record of previously inserted SIM cards, but if the carrier name of your SIM does not show up in the status bar after you changed the SIM you will need to reconnect iPhone through Wi-Fi or USB to iTunes.
If iPhone does not work with the SIM card after connecting to iTunes, you might need to restore your iPhone.
Consult the iPhone User's Guide for more information on iTunes and iPhone.
If you swap a SIM card, your visual voicemail messages may no longer be available on the iPhone.