I am a current AT&T wireless customer with an iPhone 5. I plan to buy an unlocked iPhone 7 Plus from Apple. If I don't plan to make any change to my existing plan, do I simply transfer the SIM card from the old phone to the new one? Or are there additional steps I need to take to activate the new phone (or activation fee)? Thank you.
Yes, that is all you need to do, move the SIM card. There are no additional fees. However, it is possible you have an old SIM card that does not support advanced calling services such as WiFi calling. The iPhone 7 will let you know that when you put the SIM card in. If it does and you want those advanced services, you will need a new SIM card which you can get at any ATT corporate store for $5.
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