What is a (SIM) unlock?

Cellphone operators, also called carriers (like AT&T, Verizon, Vodafone, Swisscom, Sunrise, Orange, etc.) often sell discounted devices (or even free) if you sign a contract with them for paying a monthly fee to use their services. To make sure you don't just buy their discounted mobile phone and don't use their service, they lock your device. Maybe you don't even want to switch to another carrier, but you want to use a local provider when you're on vacation in another country. In this case you cannot do that. In order to be free again, you have to unlock your device. Because an unlock requires to run unsigned code on the device, you have to jailbreak[1] it first. Sometimes you can jailbreak and unlock with the same tool.

References:

  1. What is a jailbreak?
last edit: 2011-01-02

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