If a phone displays a message asking for a PUK number, contact your wireless provider before entering any other information. Cell phones on Global System for Mobile Communications (GSM) networks use Subscriber Identity Module (SIM) cards to allow phones to communicate with the wireless network. Users can secure their phones using a Personal Identification Number (PIN). If a user enters an incorrect PIN three times, the phone will block the SIM and ask for a Personal Unlocking Key (PUK) number. If a user enters an incorrect PUK code too many times, the phone will permanently lock the SIM card.
Contact the service provider. As a security precaution, wireless providers typically do not give out PUK numbers when activating a phone. The PIN protects a cell phone from unauthorised use and the PUK serves as a backup if a user forgets the PIN. If someone steals a phone and knows the PUK, the thief can easily unlock and use a stolen phone. Wireless customers can call their providers to get the PUK code and AT&T customers can access the number through their online account. Log onto your account and select "My Services," "My Phone/Device" and "Unblock SIM Card."
Answer any security questions. If a phone asks for a PUK number, it means the user does not know the PIN. Customer service representatives will likely suspect theft and need to confirm the user's identity. Wireless providers may even have policies dictating that customer service representatives can only give the PUK to the phone's account holder.
Enter the PUK code and press "Yes/OK." The PUK code will be eight digits long and each one is unique to a SIM card. Some Motorola users have to enter *5 if the SIM is blocked, but the phone is not displaying a message asking for the PUK.
Reset the PIN. Phones ask for PUK codes because a user entered the incorrect PIN. Therefore, users need to create a new PIN in order to use the phone again.
Only GMS wireless providers use PUK codes. AT&T, T-Mobile, Nextel and some smaller providers use GSM. Verizon, Sprint, U.S. Cellular, Credo Mobile and other small providers use Code Division Multiple Access (CDMA). CDMA phones do not use SIM cards, so those phones will not ask for a PUK code.
If a user enters the incorrect PUK code a certain number of times, usually five to ten times, the phone will permanently block the SIM card. The wireless provider will likely charge the customer for a new SIM card. This means any data such as phone numbers saved on the SIM card will disappear.