You have 30 days to try a new device. So get the new phone, use it for 2 or 3 weeks, see if you like it. If not, return it and go back to your old phone, and your account will have the NE2 restored and you'll be back to where you were.
Your old phone is yours, you keep it (we have several of our old phones and they come in handy as an emergency replacement here and there!). The new phone is activated with your same number, try it out, keep it if you like it, return it if you don't.