Your network carrier identifies you via your SIM (Subscriber Identity Module). Therefore, if someone obtains your SIM, any actions they take (calls, messages, etc.) will be attributed to you.

Your phone's SIM card allows the device to make calls, send texts, and connect to the internet. The SIM card provides a phone number that identifies your device on the carrier's network, whether ...

[Jason Gin] wanted to reuse the SIM card that came with a ZTE WF721 wireless terminal he got from AT&T, but as he expected, it was locked to the device. Unfortunately, the terminal has no function ...

A PUK code is required if a GSM SIM card was locked after entering the wrong PIN code three times in a row. Entering a wrong PUK code ten times in a row disables the SIM card permanently.

If you’re thinking of moving to a new network, and want to keep hold of the same iPhone, you may hit a snag: the device is locked to your current carrier and can’t be used with any other company.