How do you switch the data plan between two iphones?

To switch the data plan between two iphones, you can use the "SIM card" method. Remove the SIM card from the iphone with the current data plan and insert it into the second iphone. Ensure the second iphone is unlocked and compatible with the SIM card. Alternatively, if both phones support eSIM, you can transfer the eSIM profile via the carrier's app or by contacting your carrier for assistance.