If you do the software update on your old iPhone, or likely new one, while the phone is in airplane mode then when you are finished it will be stuck in a loop.
The iPhone will tell you to plug it in to iTunes, iTunes will tell you it can’t access the phone till the phone is activated.
To break the loop. Go to the phone and tell it you want to make an emergency call. It will tell it must turn off airplane mode. Tell to go ahead. Then you can plug it into iTunes and everything will work itself out and be fine.