SMT-W6100 User Guide153PIN (Personal Identification Number)Security code that protects the phone/SIM against unauthorized use. The PIN is supplied by theservice provider with the SIM card. It may be a four to eight-digit number and can be changed, asrequired.PUK (PIN Unblocking Key)Security code used to unlock the phone when an incorrect PIN has been entered three times insuccession. The eight-digit number is supplied by the service provider with the SIM card.SIM (Subscriber Identification Module)Card containing a chip with all the information required to operate the phone(network andmemory information, as well as the subscriber’s personal data). The SIM card fits into a smallslot on the back of the phone and is protected by the battery.SMS (Short Message Service)Network service sending and receiving messages to and from another subscriber without havingto speak to the correspondent. The message created or received can be displayed, received,edited or sent.