How to lock SIM card in Lollipop OS based device?
You can set a lock on your SIM card so it can't be used by anyone who doesn't know the lock code. To protect your SIM card from others using it for phone calls or cellular data, you can use a SIM PIN to prevent anyone from accessing precious account information or using your data plan. Then, every time you restart your device or remove the SIM card, your SIM card will automatically lock and you'll see "Locked SIM" in the status bar.
Navigate to Apps → Settings → Lock screen and security → Other security settings → Set up SIM card lock → Activate switch → Enter PIN → Ok
Pictorial representation to lock SIM card is as follows:
a). Tap on Apps icon from the Home screen.
b). Drag the Screen upwards to access more apps.
c). Tap on Settings icon.
d). Tap on Lock screen and security settings.
e). Drag the Screen upwards to access more settings.
f). Select and tap on Other security settings.
g). Tap on Set up SIM card lock.
h). Tap on the Switch to activate Lock SIM card.
i). Enter the PIN.
NOTE : You may have to get the default SIM card pin from your carrier.
j). Tap on Ok.
Your SIM card will be locked.
CLICK HERE to know how to change SIM card lock PIN in Lollipop OS based device.