A really useful command for unlocking the SIM while in the router.
router#sh cell 0/1/0 security
Card Holder Verification (CHV1) = Enabled
SIM Status = Locked
SIM User Operation Required = Enter CHV1
Number of Retries remaining = 3
router#cellular 0/1/0 gsm sim unlock NNNN
!!!WARNING: SIM will be unlocked with pin=NNNN(4), call will be disconnected!!!
Are you sure you want to proceed?[confirm]