Why are some smartphones not compatible with certain carriers?

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Why does it matter what SIM card I put into a device?

In: Engineering

the phone is heavily subsidised by the carrier. so for that reason the handset gets locked to the network so they can recoup their investment. if you have a contract with the carrier after a period they will gife you an unlock code to remove the bar and the phone will become sim free.

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.

Or rather, why is your phone locked to a particular carrier? No smartphones that I can think of in recent memory are actually restricted to or from a carrier on the basis of technology – it used to be, CDMA vs. GSM vs. whatever… but now many mobile chipsets are capable of talking most wireless technologies and frequency bands…. back when I worked in wireless there were some differences between frequency bands between NA, Europe and Asia, so you had to have slightly different models for each market, but Im pretty sure that’s not the case anymore.

Rather, the reason your phone is locked to a carrier is because of customer-lock in. Carriers don’t actually make money on phone sales – they lose money; the phone is a loss leader to get you to sign up for a monthly plan. Thats what a Device Tab is, essentially you’re paying off the purchase price of your phone. There is also the question of carrier exclusivity – AT&T may pay Apple $$$ to be able to sell iPhoneY exclusively in the US for a time period, they don’t want you to buy an iPhoneY (remember they lose money on that) and then switch to BargainBasement Carrier, they want to keep you on $ExpensivePlan.