One handy trick I learned was that when you get a new phone with a fresh SIM card, not only lock it with a SIM PIN in settings, but call your mobile provider and get their (usually 2 I think) PUK codes. So if you or someone else accidentally locks out your SIM through unauthorized access or 3+ failed SIM PIN entries via your handset, you can unlock it again. Also in settings, turn on the option that requires you to enter your SIM PIN in order to reestablish connectivity to your carrier’s network when you power down the phone and power it back up again. It’s also a good idea to routinely call your carrier or log in to your account admin page and change the account access PIN.