3Ps_Paul Said:
"Upgrading iPhone on consumer cellular at Apple Store: I have an iPhone 14 Pro Max and Apple Watch Ultra running on Consumer Cellular. Can I upgrade to an iPhone 16 Pro Max in an Apple Store and leave the store with a phone and watching running on Consumer Cellular?"
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Walking Out with a New iPhone:
You may be able to; but, be prepared for the transfer to a new device. Your iPhone has a SIM card in the Western hemisphere, wheat it has an eSIM card in the Eastern hemisphere. So, you'd move the card to the new iPhone. I'd say, it would be wise to transfer it all with assistance of the Apple Rep, before departing the store. Perform as instructed here, including the iCloud logout and factory reset: What to do Before you Sell, Give Away, or Trade in your iPhone or iPad - Apple Support