Unlock SIM card
Most mobile company sold SIM card that comes out with a PUK (Personal Unblocking Key) code or PIN (personal identification number). The main purpose of these codes is to provide a security so the mobile owner data and information is protected against anyone to stealing his personal information or read his private messages without his permission. As a general rule most mobile companies make a GSM phones with Sim lock built in capability which restrict a mobile user use limited to countries and network provider. In this way phone is most program to accept only Sim card that are intended to use for a specific countries.
You could upgrade your mobile for roaming capability for added services but usually when you come to other countries you need to buy another Sim card compatible with the networks providers in the countries you go.
The responsibility of unlocking a Sim card could fall under the responsibility of the mobile user with voluntary or either a mandatory requirements. Most networks require their clients under a post paid subscription to unlock their Sim card provided they have an account for at least 90 days. The codes that are includes upon purchase of the Sim card were normally given or change later by the subscriber are generated to prevent your SIM card from unauthorized use, theft or loss.
The PUK is normally included in a machine-generated security paper. Make sure to memorize the PUK code or stored the important copy in undisclosed place. In USA unlocking a Sim card is generally legal. You would know a Sim card is unlock when you press certain codes key to unlock it by providing a password or certain hidden character only known to you. You need to keep it secret and not allow anyone to know it to disallow thief from peeping or stealing your mobile data.
Remember that a PUK code has nothing to do with your mobile phone brand as it is tied to the Sim card itself. In case you lost or forgot your PUK code of your Sim card. To unlock a Sim card you could still retrieve them by calling your mobile subscriber to authenticate your identity and they would provide you with your with new PUK code for your Sim card.
As a post paid subscriber this could be easily done by identifying or providing your mobile number. In case you are a pre paid subscriber there is no way to retrieve your PUK code unless you could provide the form included when you buy your Sim card. It is very cheap now days to buy another Sim card just be sure you have back up your contact number you got not lost connection with them. Remember that the care and protection of your mobile depend over all in your care and concern to install maximum security password to avoid phishing scam or anyone to steal your precious data and information.