iPhone 17 Christmas Gift for Wife. Help!

Edit: Thanks for the responses everyone! I believe I will just upgrade my line and then call Verizon and have them switch lines after Christmas.

—————————————————————————— I have been with Verizon for about twenty years. My wife has an iPhone 13 that she has had for about several years. I want to upgrade her to a new iPhone 17 Pro max and give it to her on Christmas morning without her knowing anything about it ahead of time.

I went to a Verizon store today and they told me I could buy the new phone now and bring her old iPhone 13 back later for the trade in. The problem is that they said it will send a message to her current phone once the new one is tied to her line. It will say something like welcome to your new phone and it would also force her to reset her phone and download the digital sim again. If that happens she will know I bought her a new phone and the surprise is ruined.

I want to stay on the monthly payment plan. I do not want to buy the phone outright. My only goal is to keep everything a perfect secret until Christmas morning. How do I get the new phone added to my account with the trade in deal and avoid any alerts or changes hitting her current phone until I am ready to activate the new one on Christmas.

Is there a way to upgrade the phone and keep it unactivated and unassigned until I give it to her. Or is there another way that still keeps her from finding out?