A:AnswerIt depends on the carrier. Best Buy does sell some carrier specific phones, but the unlocked phones probably won't allow you to get the carrier trade-in offers. You should check with Best Buy.
A:AnswerNo. Your headphones will need to be Bluetooth or USB-C. I have a small dongle for the USB-C port that has USB-C and headphone jack, so that I can charge my phone and use a wired headset if necessary. Just Google "usb-c to usb-c and headphone" for examples.
A:AnswerI had zero issues moving my Verizon number to my new Pixel 10. It was a fully automated process moving from my Samsung Galazy A16 to my new Pixel 10.