Why does it matter what SIM card I put into a device?
In: Engineering
It’s not so much the SIM card as it is the radio frequencies and the communications protocol that each carrier uses. On the older systems there were two main protocols, CDMA and GSM, and they were not compatible at all. In about 2010, LTE became the dominant protocol, and the CDMA and GSM networks are beginning to go the way of the dodo bird, with all but a few planned for shutdown by the end of 2020. That will take away the protocol problem, but the frequency problem will still be there, because different carriers are allotted different frequencies for operation.
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