It all depends on your current Cellular carrier. Each of often have a different process vs the default Apple iPhone process that runs as part of the iPhone to iPhone transfer process.
I have straight talk.
Well Straight Talk does not support the Apple iPhone transfer process. You will need to use their Activation process. Here is a link to review:
What would you be trading in and where would you want to perform and trade in?
I never had a "plan". I always just went to the store and bought those cards and reload the phone every month.
Not sure how things work in your area. Where I live you call your carrier and tell them you need an e-sim. They then help you with it🤷🏻♂️
Most cases carriers have an app. You install that to activate your phone. And you transfer the physical to eSIM. I’ve done this method and reverse (esim to physical sim)
When I got my sim card transferred to my old phone, for example, I never had an app to activate the phone.
Assuming you buy your phone at an Apple store. The process is easy, you unlock the old phone and hand it to the salesperson. He "does stuff", asks you to enter a password, and then hands you back a new working 16e and a deactivated old phone (that still works except for the cell phone function.)
