If you get the serial number before then, you can. But if not, when it arrives, you can call Apple and have it added. in fact, you can do so anytime during the first year.
You can add it after you receive it, even if you open it and use it. Just as long as your phone isn't damaged. You can also add AppleCare Plus via the Apple Support app.
You can add it after you receive it, even if you open it and use it. Just as long as your phone isn't damaged. You can also add AppleCare Plus via the Apple Support app.
Yes you can purchase AppleCare plus through the Apple Support app, or by calling and they will run some diagnostic test on your device and if it passes then they will go ahead and add the AppleCare+ to your phone.