from an iPhone 6S to an iPhone SE
my new iphone SE already has a SIM card in it. Do I replace it with my old iphone SIM card??
I don't know, this is a user to user community.
If you bought a new contract with a new phone, then you need to use the new sim.
If you bought it from Apple then you can put the new sim in.
It sounds like if your device has a Sim in it, sounds like you might have a new contract or number, but only you can know this answer
