Why are some Phones Locked and Unlocked

The term GSM means - Global System for Mobile Communications. It is the most popular standard for mobile phones in the world. GSM differs significantly from its predecessors in that both signaling and speech channels are Digital call quality, which means that it is considered a second generation (2G) mobile phone system. GSM is an open standard which is currently developed by the 3rd Generation Partnership Project (3GPP).
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