I'm still trying to wrap my brain around how this works, and I shouldn't be doing that at this late after the day I've had. So I'll save those questions for later.
But do I understand that when you are ready to get your new phone, you must trade in your old phone. So if I have an S4 and want an HTC One, I will not end up with both even having paid for them? because I will have to trade in S4.