Swapping SIM cards between cell phones

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first questions: you have identical phones, but are they from the same provider? if yes, then just swap the SIMS and you're good to go. If they are not from the same provides (even though that are identical models otherwise), you need to unlock the phones first. Just call each provider and ask them for the code.

second questions: yes, a used phone from the same provides will work with your SIM card. It can even be a different brand, you don't have to stick so Samsung.


BTW: just swapping SIM cards will not damage anything, unless you try to use one of those SIM cards readers/writers to edit information on the SIM card, then it gets tricky.