Many users face the problem of locking their phones by mistake. A PUK code is a cell phone safety mechanism provided by the network company. This is to protect your data in case of mobile phone theft or its unauthorized. This code changes every month, and you can get it only from the customer care center of the service provider. Explanation For AT&T SIM cards, a PUK code is required when one feeds in the wrong PIN code for the card, three times in succession. If you forget your PIN code or another person tries to put in the wrong code, it results in locking up of your phone. The only way to unlock it is by entering the PUK code. This is a unique code, and you can locate it on the card certificate that comes along with your SIM card. However, many times people tend to misplace these certificates, and cannot find the code. You can call up the customer service center from another phone, and speak to them about your problem. The assistant or executive will ask you a few questions to be sure that you are the owner of the phone. Then, he/she will provide you with the unique 8 digit PUK code, which you can enter into your mobile phone directly. Then, you need to press 'OK', and you will be prompted to enter the code again. This is done to verify your code properly. However, in some handsets, you may require to dial **05*(PUK Code)*(New PIN)#[Send]. You can refer to your handset model for further instructions, and enter the code accordingly. If you do not wish to dial the customer care number, and still get your code, you can visit the website of AT&T. Log on into the section My Wireless Account and click on the My Services tab. Then, you need to click My Phone/ Device, and look for the link that says Unblock SIM Card. You will get a pop-up page that provides all the details of your phone, along with your name and phone number. This page will also provide your PUK Code. If you look further down the page, you will find instructions on how to unblock your SIM card. Follow the instructions carefully, and your phone will be unlocked in minutes. While entering the code, keep in mind that you do not enter the wrong number, and also, do not try and guess it. This is because, if you enter the wrong code ten times successively , this will result in permanent locking of your SIM, and then you have to replace it with a new one.