Do I have to switch my SIM card from my iPhone 11 Pro to my new iPhone 12 Pro?
Do I have to switch my SIM card from my old iPhone 11 Pro to my new iPhone 12 Pro to set up new iPhone ??
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iPhones do not store anything on the SIM card.
Moving the SIM card is the fastest and easiest way to activate your cell service.
To activate your phone it has to have a SIM card inserted.
To transfer settings and data see this:
Use Quick Start to transfer data to a new iPhone, iPad, or iPod touch - Apple Support