Transfer Data
Can I continue to use my old iPhone if I transfer my data to a new iPhone I haven’t activated yet?
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Hello,
Yes, you can continue to use the old phone. In fact, you can use both phones going forward. Once cellular service has been transferred to the new phone, the old phone will continue to work as a communication device. You just won't be able to make voice calls on the old phone. Almost everything else will continue to work.
See this for transferring your data:
Transfer content from your previous iOS device to your new iPhone, iPad, or iPod touch
Good luck.