SIM card

Swapping the SIM card does not alter an iPhone setup, though an iPhone does require a cellular plan for activation.

The new iPhone must either be unlocked, or the SIM must match the carrier holding the carrier lock, if the iPhone is carrier locked.

That depends on your carrier. Some expect a physical SIM transfer, some will transfer the cellular plan electronically, some require the plan be transferred electronically seemingly so that they might acquire a transfer fee.

The choice is yours.